Not long ago, I was at a dinner party with several couples in their 40s, all married except for my boyfriend and me. The mood was jovial until, over dessert, one guest made an offhand joke about Internet porn.

His wife took issue, and during a tense back-and-forth between them, the rest of us sensed that we were about to learn way too much about their personal lives. Fortunately, another husband deftly maneuvered to a safe topic for middle-aged parents (kids and screen time!), and after a lively discussion about iPads, we made our excuses to leave.

In the car, I turned to my boyfriend and said, “I bet there won’t be any sex happening in their bedroom tonight.”

He smiled and shook his head. He predicted that the hosts would be the least likely to have sex that night.

I thought he was kidding. This couple were my “model marrieds,” true equals who share the housework and child care, communicate openly and prioritize each other’s careers. The best friends of happy-couple cliché. Earlier in the evening, I watched them work together in the kitchen, cheerfully cooking and cleaning: She bringing out the hors d’oeuvres, and he chopping and dicing. When their 6-year-old woke up with a nightmare, they wordlessly agreed that he would be the one to soothe her. It was the kind of marriage many people wish for.

“Exactly,” my boyfriend said. “Least likely.”

Marriage is hardly known for being an aphrodisiac, of course, but my boyfriend was referring to a particularly modern state of marital affairs. Today, according to census data, in 64 percent of U.S. marriages with children under 18, both husband and wife work. There’s more gender-fluidity when it comes to who brings in the money, who does the laundry and dishes, who drives the car pool and braids the kids’ hair, even who owns the home. A vast majority of adults under 30 in this country say that this is a good thing, according to a Pew Research Center survey: They aspire to what’s known in the social sciences as an egalitarian marriage, meaning that both spouses work and take care of the house and that the relationship is built on equal power, shared interests and friendship. But the very qualities that lead to greater emotional satisfaction in peer marriages, as one sociologist calls them, may be having an unexpectedly negative impact on these couples’ sex lives.

A study called “Egalitarianism, Housework and Sexual Frequency in Marriage,” which appeared in The American Sociological Review last year, surprised many, precisely because it went against the logical assumption that as marriages improve by becoming more equal, the sex in these marriages will improve, too. Instead, it found that when men did certain kinds of chores around the house, couples had less sex. Specifically, if men did all of what the researchers characterized as feminine chores like folding laundry, cooking or vacuuming — the kinds of things many women say they want their husbands to do — then couples had sex 1.5 fewer times per month than those with husbands who did what were considered masculine chores, like taking out the trash or fixing the car. It wasn’t just the frequency that was affected, either — at least for the wives. The more traditional the division of labor, meaning the greater the husband’s share of masculine chores compared with feminine ones, the greater his wife’s reported sexual satisfaction.

Granted, some might view a study like this with skepticism. Correlations don’t establish causation, and especially when it comes to sex, there’s always a risk of reporting bias and selective sampling, not to mention the mood of a subject at the time of the survey. (Was she answering the questions while standing next to a big pile of garbage that hadn’t been taken out?) What’s more, while this study used the most recent nationally representative data that included measures of sexual frequency and a couple’s division of labor, it was drawn from information collected in the 1990s. (Julie Brines, an author of the chores study, explained, however, that many studies on housework since then show that not much has changed in terms of division of labor.) But as a psychotherapist who works with couples, I’ve noticed something similar to the findings. That is, it’s true that being stuck with all the chores rarely tends to make wives desire their husbands. Yet having their partner, say, load the dishwasher — a popular type of marital intervention suggested by self-help books, women’s magazines and therapists alike — doesn’t seem to have much of an effect on their libido, either. Many of my colleagues have observed the same thing: No matter how much sink-scrubbing and grocery-shopping the husband does, no matter how well husband and wife communicate with each other, no matter how sensitive they are to each other’s emotions and work schedules, the wife does not find her husband more sexually exciting, even if she feels both closer to and happier with him.

In one study, 34 percent of adulterous women said they were ‘happy’ in their marriages.

I first noticed this while doing a yearlong training in marriage therapy. I was seeing a couple who had been married for five years and wanted to work out some common kinks related to balancing their respective jobs, incomes and household responsibilities in, as the wife put it, “an equal way.” Over the course of treatment, the couple reported more connection, less friction and increased happiness. One day, though, when their issues seemed largely resolved and I suggested discussing an end to their therapy, the husband brought up a new concern: His wife now seemed less interested in having sex with him. He turned to her and asked why. Was she still attracted to him? After all, he wondered, why did she appear less interested now that their relationship seemed stronger in all the ways she wanted?

“I’m very attracted to you,” she said earnestly. “You know when I really crave you? It’s when you’re just back from the gym and you’re all sweaty and you take off your clothes to get in the shower and I see your muscles.”

Her husband countered by saying that this very situation had occurred that morning but that his wife became irritated when he tossed his clothes on the floor, which led to a conversation about his not vacuuming the day before, when she worked late. He had worked late, too, which accounted for the lack of vacuuming, but still — she hated waking up to a messy room, and it was his turn to vacuum.

“Right,” she agreed. “I wasn’t focused on sex, because I wanted you to get out the vacuum.”

“So if I got out the vacuum, then you’d be turned on?”

His wife thought about it for a minute. “Actually, probably not,” she said slowly, as if hearing the contradiction even as she was speaking it. “The vacuuming would have killed the weight-lifting vibe.”

Brines believes the quandary many couples find themselves in comes down to this: “The less gender differentiation, the less sexual desire.” In other words, in an attempt to be gender-neutral, we may have become gender-neutered. It’s interesting to note that when I asked Justin Garcia, a research scientist at the Kinsey Institute, whether lack of gender differentiation affects the sex lives of gay couples, he said that male couples, who have more sex than lesbian couples, tend to differentiate by choosing partners sexually unlike themselves — who, say, want to be in the more submissive sexual position — and that lesbians don’t follow as much of a pattern of seeking their sexual opposites. I posed the same question to Pepper Schwartz, a sociology professor at the University of Washington who coined the term “lesbian bed death,” and she pointed out that gay male couples differentiate from each other in other ways, too. For gay men, she said, “the initial filter is erotic, so they’re more likely to end up with somebody who’s very different in terms of education or social class.” But, she continued, “a gay woman thinks like the heterosexual woman who asks: ‘Do we share common goals? Do we like to do things together? Is he smart?’ ” She believes that lesbian and heterosexual couples share sexual challenges because both relationships involve women who tend to seek similar mates. As she put it, most men, regardless of sexual orientation, prioritize the erotic, but “heterosexual men have to deal with heterosexual women.”

This isn’t to say that egalitarian heterosexual couples aren’t happy. Lynn Prince Cooke, a professor of social policy at the University of Bath in England, found that American couples who share breadwinning and household duties are less likely to divorce. And Stephanie Coontz, author of “Marriage, a History,” told me that having a partner who does housework and child care has become a bigger factor in women’s marital satisfaction than many other factors that used to predict marital happiness, like a man’s level of income or shared religious beliefs.

The chores study seems to show that women do want their husbands to help out — just in gender-specific ways. Couples in which the husband did plenty of traditionally male chores reported a 17.5 percent higher frequency of sexual intercourse than those in which the husband did none. These findings, Brines says, “might have something to do with the fact that the traditional behaviors that men and women enact feed into associations that people have about masculinity and femininity.” She calls these associations and behaviors sexual scripts. Men and women, she said, are continuously sending out cues that signal attractiveness to a potential partner, and often these cues involve “an ongoing reminder of difference and the sense of mystery and excitement that comes with the knowledge that the other person isn’t you.” When I asked Esther Perel, a couples therapist whose book, “Mating in Captivity,” addresses the issue of desire in marriage, about the role sexual scripts play in egalitarian partnerships, she explained it like this: “Egalitarian marriage takes the values of a good social system — consensus-building and consent — and assumes you can bring these rules into the bedroom. But the values that make for good social relationships are not necessarily the same ones that drive lust.” In fact, she continued, “most of us get turned on at night by the very things that we’ll demonstrate against during the day.”

23 percent of married mothers have a higher income than their husbands.

Power — and the act of balancing it — is a common topic with the couples I see in therapy. They’re eager to talk about leveling the domestic playing field but tend to feel awkward about bringing the concept of power into conversations about sex, mostly because it can feel so confusing.

One woman in her late 30s, for instance, who has been in a peer marriage for 10 years, said during couples therapy that when she asked her husband to be more forceful, “rougher,” in bed, the result was comical.

“He was trying to do what I wanted,” she explained, “but he was so . . . careful. I don’t want him to ask, ‘Are you O.K.?’ I want him not to care if I’m O.K., to just, you know, not be the good husband and take charge.” And yet, she said, his caring and his concern that she’s O.K. with what he’s doing are what she loves so much about him in every other area of their marriage, ranging from which brand of toilet paper to buy to what to feed their children to where their money is spent and which nights each of them can stay late at work. “I don’t want him to take charge like that with anything else!” she said.

I mentioned this situation to Dan Savage, the sex columnist, who told me that he sees similar themes in the letters he receives and the questions he fields at personal appearances. At a recent talk, for instance, one woman asked him if a certain sex act was “loving or degrading?”

“My reply was, ‘Yes,’ ” he told me. “Why can’t it be both?” He continued: “People have to learn to compartmentalize. We all want to be objectified by the person we love at times. We all want to be with somebody who can flip the switch and see you as an object for an hour. Sometimes sex is an expression of anger or a struggle for power and dominance. They work in concert. People need to learn how to harness those impulses playfully in ways that are acceptable in equal relationships.”

A desire for equality, and the lack of desire that equality can create, may make scientific sense, even as it challenges conventional wisdom. As Daniel Bergner has written in his book “What Do Women Want?” and in this magazine, many studies show that women often report fantasies, like those involving submission, that tend to be inconsistent with our notion of progressive relationships.

But Pepper Schwartz says that while women may have always had these types of fantasies, now they have permission to give voice to them because of how much power they have in real life. “The more powerful you are in your marriage, and the more responsibility you have in other areas of your life, the more submission becomes sexy,” Schwartz says. “It’s like: ‘Let me lose all that responsibility for an hour. I’ve got plenty of it.’ It’s what you can afford once you don’t live a life of submission.” Married women, she adds, may have had a very different relationship to their fantasies back in the ‘50s, but even so, “this mixture of changing gender roles and sexual negotiation is tricky.”

So tricky, in fact, that when I was speaking about relationships at a conference and mentioned that I was writing about this topic, a large group of women who had just waxed poetic about “Fifty Shades of Grey” suddenly seemed outraged. Was I saying people can’t have good sex in egalitarian marriages? (No, I wasn’t.) Isn’t marriage better over all when partners have equal power? (In my opinion, yes.) Then why write about this kind of thing? (Because when a roomful of women who just raved about “Fifty Shades of Grey” don’t want me to write about “this kind of thing,” that tells me it should be talked about.)

Men, of course, can feel just as uneasy with overt expressions of power in marriages that are otherwise based on equality. During a couples session, one woman in her early 40s said that it wasn’t until she came across some porn scenes her husband had viewed online that she felt comfortable telling him about her fantasies, which happened to be very similar to what she found. She thought he’d be thrilled, but although he enacted the scenes with her, she was surprised by his lack of enthusiasm.

“I felt like he was just doing it because I asked him to, not because he wanted to,” she said. I wondered if she was putting her husband in a double-bind, analogous to, “He bought me flowers on Valentine’s Day because he knows he’s supposed to — not because he really wants to.”

No, she said. It was something else: It bothered her that her husband acknowledged being turned on by watching the fantasy online but not by doing it in real life with her. “I felt so rejected,” she said. “I told him, ‘I want you to want to dominate me,’ but he said he just doesn’t see me that way, that he doesn’t see us that way.”

For this couple, the experiment felt so awkward that they quickly reverted to their routine: sex in the usual roles and positions during a window between 10:30 and 11 p.m. when they were both tired but not yet asleep. When I turned to her husband for his perspective, he seemed relieved that he could express his puzzlement.

“It’s nice,” he said about the sex they have. “It’s not superhot all the time, but it’s really nice. I’m attracted to her, and I like being with her, and I’m very happy with our sex life. I don’t know what she expects. If I don’t clean up the bathroom, if I don’t give her equal time with her work, if I make a decision without consulting her, she wouldn’t want that. I’m so used to interacting with her as an equal — and I also want that — but I like what we have, and occasionally I like getting the other stuff on the Internet. Isn’t being a good husband and father and wanting to have semirespectful sex with my wife enough? Before we got married, we always said we’d have a 50-50 marriage, and you’d think that would be great for our sex life, but instead it’s the one area where we’re having trouble. Everything else is great. It’s the sex we don’t agree on.”

He took a deep breath before adding: “I know what a 50-50 marriage should be like. But what is 50-50 sex supposed to be like?”

Sex in any marriage is idiosyncratic and complex — and if it’s consensual and enjoyable, it’s nobody’s business, frankly. But the idea that married sex should be steamy is reflected in our culture. Take the fascination with MILFs — consistently one of the most-searched porn categories and a staple in mainstream media — in which mothers are depicted as alluring and sexually lively. In the past, a fantasy woman may have been the young, single secretary; now she’s the middle-aged mother of three with a graduate degree. In a way, this might seem like an encouraging shift for married moms. Instead of becoming invisible, we’re wanted and capable of doing it all: work, play dates and having hot sex lives. But these sorts of portrayals also create a false sense of reality.

“The passionate marriage used to be a contradiction in terms,” Esther Perel, the couples expert, told me. The quality of sex in marriage — and not just the frequency — is a relatively new conversation that has come about with more egalitarian marriages. In today’s marriages, she said, “we don’t just want sex; it has to be intimate sex. It has to be transcendent and self-actualizing.”

‘The values that make for good social relationships are not necessarily the same ones that drive lust. Most of us get turned on at night by the very things that we’ll demonstrate against during the day.’

Which brings me back to the dinner party where that husband made a joke about Internet porn. The conversation started innocuously enough, with the husband making the observation that with men and women both balancing the responsibilities of work and household, even sex needs to be outsourced sometimes. By day’s end, he said, men feel so worn out that they, too, “get headaches” because they don’t necessarily have the energy to make sex happen or, more specifically, to make it happen in the way their wives want it to. The modern marital tableau, he quipped, is two overwhelmed people trying to relax before bed: he on Pornhub, she on Pinterest. Then they kiss and go to sleep.

The men at the dinner party laughed; the women smiled uneasily. His wife seemed perplexed. If men found release on Pornhub, what about women’s sexual needs? That’s when things got dicey. Without missing a beat, the husband deadpanned, “Vibrators do for modern men what dishwashers did for modern women.” His wife became upset, calling the comment “selfish.” He defended himself by saying that he gives his wife frequent back rubs, while she has given him a massage “maybe 10 times in our entire marriage.” (Every man at the table nodded in recognition.) As we averted our gazes, I’m guessing we were all thinking the same thing: How impossible it often feels for two exhausted equals to meet each other’s sexual needs.

Porn, of course, doesn’t tend to be about reciprocity. “Here’s the essence of porn,” Terry Real, a couples expert in Boston, told me. “What will you never see in a porn video? ‘Honey, I don’t like that, could you stop doing that, could you take a shower first?’ The archetype of the porn queen is that she’s a woman who derives sexual pleasure by giving the man pleasure, and — here’s the key — everything he does is absolutely perfect! What you don’t see in porn is anything that needs to be negotiated, the woman having needs of her own or the roles being reversed.”

In other words, it’s the antithesis of peer marriage. In “Marriage: A History,” Coontz writes that one recent marital development “is that husbands have to respond positively to their wives’ requests for change.” Yet no matter how many requests wives make and how hard their husbands try to accommodate them, the women may still end up disappointed. After all, women are now coming into marriage with sexual histories and experiences on par with men’s, leading to expectations that are difficult to replicate in any marriage, especially now that people live longer and will be having sex, presumably with the same person, for decades more.

Similarly, older c​ouples who can now wait and marry for love have less time together during their sexual primes and, if kids are in the plan, they may even miss that year or two of newlywed abandon. (Ask a 40-year-old couple trying and failing to conceive how much fun the sex is.) Pepper Schwartz, who serves as AARP’s relationships expert, observes that 50-year-olds of the past were often grandparents without great expectations about their sex lives. Now those same 50-year-olds might have a 10-year-old, placing them in a life stage formerly occupied by people in their 30s and subjecting them to pressure to maintain the culture’s view of “youthful sexuality” in marriage, especially with the ubiquity of Viagra and Estrace.

One day I was talking about these expectations with a friend, a 41-year-old married father. He and his wife, who have two young children, are in a minority in their Los Angeles social circle: She takes care of the house and kids, and he provides all of the income. He said that he and his wife consider their sex life to be good.

“We use X number of positions and various forms of oral and manual stimulation, and we’re happy as clams,” he said. “But a lot of people think it’s supposed to be more exciting than this.”

He believes that we have to accept that we’re not going to get everything we want in our marriages and our sex lives, instead of constantly complaining about it or wondering if we might not be compatible with our spouse. “How much are you going to let the 10 percent of your differences dictate your future?” he asked. “Is anal sex more important than your marriage?”

I shared my friend’s observation with Helen Fisher, a senior research fellow at the Kinsey Institute who studies sexual attraction. She noted that even people who are satisfied with their sex lives often crave more nowadays. She told me about a study she conducted that asked participants who had had affairs why they did so. Fifty-six percent of her male subjects and 34 percent of her female subjects said they were “happy” or “very happy” in their partnerships but cheated anyway.

While past research has shown that men have higher rates of infidelity than women, those rates are becoming increasingly similar, particularly in younger people in developed countries, where recent studies have found no gender differences in extramarital sex among men and women under 40. This may be because younger women are more likely to be in peer marriages — and conditions in peer marriages make female infidelity more probable than in traditional ones. A large national study in the late 1990s found that women who were more educated than their husbands were more likely to engage in sexual infidelity than if they were less educated than their husbands. Studies also find that people who work outside the home and whose partners remain in the home cheat more — and the traditional gender roles in this situation are now frequently reversed. As women increasingly work in professions that are not female-dominated, they have more sexual opportunities with peers than ever.

Helen Fisher told me that women’s expectations for sexual fulfillment are changing so much that when she conducted a survey last year asking, “Would you make a long-term commitment to someone who had everything you were looking for but to whom you did not feel sexually attracted?” the least likely group to say yes was women over 60. At any age, companionship, it seems, is no longer enough of a draw on its own.

There’s a phrase I often use in therapy with couples: “competing needs.” What do partners do when they have needs that directly conflict with those of their spouses? What if both have to work on the same weekend or be out of town at the same time? Who goes to the school play or compromises without feeling resentful? It used to be that husbands and wives operated largely in their own spheres with so little overlap that these questions rarely came up. But women now make up almost half of the U.S. labor force, and 23 percent of married mothers with children under 18 have a higher income than their husbands. In fact, total income is higher in families in which the woman is the primary breadwinner. When a 2010 study of business-school graduates asked, “What is success to you?” surprisingly, it was more women than men who chose “career goals,” while more men than women picked “personal growth.”

As Sheryl Sandberg encourages women to “lean in” — by which she means that they should make a determined effort to push forward in their careers — it may seem as if women are truly becoming, as Gloria Steinem put it, “the men we want to marry.” But these professional shifts seem to influence marital stability. A study put out last year by the National Bureau of Economic Research shows that if a wife earns more than her husband, the couple are 15 percent less likely to report that their marriage is very happy; 32 percent more likely to report marital troubles in the past year; and 46 percent more likely to have discussed separating in the past year. Similarly, Lynn Prince Cooke found that though sharing breadwinning and household duties decreases the likelihood of divorce, that’s true only up to a point. If a wife earns more than her husband, the risk of divorce increases. Interestingly, Cooke’s study shows that the predicted risk of divorce is lowest when the husband does 40 percent of the housework and the wife earns 40 percent of the income.

Ian Kerner, a sexuality counselor and the author of “She Comes First,” sees couples struggle to find a ratio that works. “I work a lot with stay-at-home dads and men who work from home,” he said, “and one thing I hear a lot is that in theory they’re really happy balancing flexible work with stay-at-home responsibilities, while their wives are out working full-time in corporate jobs. But at the same time, a common complaint is that Mom comes home and feels guilty for being away all day, and so much time has to be made up connecting with the children, who take first priority, that these dads feel lost in the mix.” In many couples, Kerner says, the wives start to feel disgruntled because their husbands get to see more of the kids, and the husbands, whose wives are controlling more of the spending, start to feel “financially emasculated.” Sometimes, he says, a vicious cycle begins: The husband feels marginalized and less self-confident, which causes the wife to lose respect for and desexualize him. Under these circumstances, neither is particularly interested in sex with the other.

A writer who works from home in New York told me that was exactly what happened when he reduced his work hours and took on child-care responsibilities so that his wife could rise to partner at her company. According to him, she said, “When we met, you said this was going to be a two-income family.” And he said: “It is! Your income is bigger because I take care of the kid.” They would talk about it — given his flexibility, they both agreed it made more sense for him to do more at home — but the tension would resurface, and ultimately they stopped having sex.

Now that they are divorcing, he’s still confounded. “For all the men from the days of ‘Mad Men’ who felt like the woman’s place was in the home, all the sexist troglodytes who might have thought that way, or even the enlightened men who cared deeply about their partners’ happiness,” he said, “you could round up a thousand of them, and not one would say the woman should watch the kids, clean the house, do the cooking and at the same time make the same amount of money as the guy. So when my wife had those expectations, it seemed a bit unrealistic. She’d say, ‘I work 10 hours a day.’ I’d say, ‘I work 16, and half of those I don’t get paid for.’ ”

Husbands who cook, vacuum and do laundry have sex 1.5 fewer times per month than those who do not.

Certainly, there are couples who have no problem with, and even genuinely enjoy, these types of arrangements. But frequently I hear from husbands and wives who say they want progressive marriages, in which women have the option to do anything their husbands do and vice versa, then start to feel uncomfortable when that reality is in place. And that discomfort, more often than not, leads to less sexual desire — on both sides.

Recently, a male therapy client who came to me because he began feeling depressed said that he had tremendous empathy for what women have been voicing all these years. “I have to hold down a job, I have to juggle the kids’ schedules, I have to get dinner on the table three nights a week, I have to volunteer at school, I have to get the bills sent in each month and on top of this I have to be the fun dad and the sensitive husband and then be ready to romance my wife if I want sex before bed — usually after listening to the rundown of her day and going over the list of what needs to happen the next day,” he said. “I rarely even have time to get to the gym, which is the one thing that relieves my stress.” As he tries to balance work and parenthood and his marriage and household responsibilities, he’s going “a bit mad — and I mean that in both senses of the word.”

I asked how interested he was in having sex with his wife, and he looked at me and laughed.

I met my boyfriend online, and like many marriage-minded people clicking on search criteria, I was seeking a partner similar in intellect, background and interests. I shared this with Betsey Stevenson, a well-known economist who studies relationships and whose egalitarian partnership was profiled in The New York Times two years ago, and asked how she feels about so much similarity. In her view, she said, going through life with a peer is a positive development.

“It used to be,” she explained, “that you lived your life in one way, and he lived his in another. With equal partners, there’s more of a sense of people who are kindred spirits. Now you have people who have similar interests and lifestyles.”

On an emotional level, “kindred spirits” sounds lovely. But when it comes to sexual desire, biology seems to prefer difference. Helen Fisher, for one, pointed me to the famous “sweaty T-shirt” experiment, conducted in 1995 by the Swiss researcher Claus Wedekind. He had women sniff the unwashed T-shirts of various men and asked them which scent they were most attracted to. Most women selected the T-shirts of men with genes markedly different from their own in a certain part of the immune system. Other studies confirmed these findings. Presumably this attraction to genetic variation is an evolutionary adaptation to prevent incest in our ancestral environments and improve the survival prospects of offspring. Interestingly, a later experiment found that women partnered with men who had genes similar to their own in this part of the immune system were more likely to be unfaithful; and the more of these genes a woman shared with her partner, the more she was attracted to other men.

There’s an important exception, though. These findings didn’t apply when women were on the birth-control pill: They responded differently to the T-shirt test by selecting partners who had similar immunity and were less “other.” One study even suggested that when “a woman chooses her partner while she is on the pill and then comes off it to have a child, her hormone-driven preferences change, and she may find she is married to the wrong kind of man.”

Of course, we are not driven by biology alone. There were certainly some cultural factors that caused us to choose difference in the past. Until recently, Stephanie Coontz said, “the idea was that you’re only half a person and you can’t be complete unless you get the opposite half. Both men and women were trained to find attractive somebody who did things and had things and were things that they were not.” But now that women do and have and are many of the things that they used to seek in their partners, Pepper Schwartz says that a result can be something more siblinglike than erotic. Her research likewise suggests that too much similarity in egalitarian marriages leads to boredom and decreased sexual frequency. “When you’re best friends with your partner, there’s less frisson,” Schwartz says. “Introducing more distance or difference, rather than connection and similarity, helps to resurrect passion in long-term, stable relationships.” She also found that in lesbian couples in which there’s a high degree of intimate conversation, there’s less sex.

And yet a married friend who described his wife as his “best friend” said he was happy to take a high degree of simpatico over a high degree of sexual pull. “I can walk down the street and be attracted to 10 people and want to have sex with them,” he said, “but it doesn’t mean they’re going to make me happy. It doesn’t mean I’d want to live the day-to-day with them. There are always going to be trade-offs.”

Is the trade-off of egalitarian marriage necessarily less sexual heat? It’s possible that the sexual scripts we currently follow will evolve along with our marital arrangements so that sameness becomes sexy. Regardless, more people marrying today are choosing egalitarian setups for the many other benefits they offer. If every sexual era is unhappy in its own way, it may be that we will begin to think of the challenges of egalitarian marriages less as drawbacks and more like, well, life, with its inherent limitations on how exciting any particular aspect can be.

“It’s the first time in history we are trying this experiment of a sexuality that’s rooted in equality and that lasts for decades,” Esther Perel said. “It’s a tall order for one person to be your partner in Management Inc., your best friend and passionate lover. There’s a certain part of you that with this partner will not be fulfilled. You deal with that loss. It’s a paradox to be lived with, not solved.”