One of the more interesting facts in Esther Perel's new book, State of Affairs: Rethinking Infidelity, comes near the beginning.

Since 1990, notes the psychoanalyst and writer, the rate of married women who report they've been unfaithful has increased by 40 percent, while the rate among men has remained the same.

More women than ever are cheating, she tells us, or are willing to admit that they are cheating -- and while Perel spends much of her book examining the psychological meaning, motivation, and impact of these affairs, she offers little insight into the significance of the rise itself.

So what exactly is happening inside marriages to shift the numbers? What has changed about monogamy or family life in the past 27 years to account for the closing gap? And why have so many women begun to feel entitled to the kind of behavior long accepted (albeit disapprovingly) as a male prerogative?

These questions first occurred to me a few years ago when I began to wonder how many of my friends were actually faithful to their husbands.

From a distance, they seemed happy enough, or at least content. Like me, they were doing the family thing. They had cute kids, mortgages, busy social lives, matching sets of dishes. On the surface, their husbands were reasonable, the marriages modern and equitable. If these women friends were angry unfulfilled or resentful, they didn't show it.

Is my husband having an affair?

Then one day, one of them confided in me she'd been having two overlapping affairs over the course of five years.

Almost before I'd finished processing this, another friend told me she was 100 percent faithful to her husband, except when she was out of town for work each month. Not long after, another told me that while she'd never had sex with another man, she'd had so many emotional affairs and inappropriate email correspondences over the years that she'd had to buy a separate hard drive to store them all.

What surprised me most about these conversations was not that my friends were cheating, but that many of them were so nonchalant in the way they described their extramarital adventures. There was deception but little secrecy or shame.

Often, they loved their husbands but felt in some fundamental way that their needs (sexual, emotional, psychological) were not being met inside the marriage. Some even wondered if their husbands knew about their infidelity, choosing to look away.

"The fact is," one of these friends told me, "I'm nicer to my husband when I have something special going on that's just for me." She found that she was kinder, more patient, less resentful, "less of a bitch." It occurred to me as I listened that these women were describing infidelity, not as a transgression but a creative or even subversive act, a protest against an institution they'd come to experience as suffocating or oppressive.

In an earlier generation, this might have taken the form of separation or divorce, but now, it seemed, more and more women were unwilling to abandon the marriages and families they'd built over years or decades. They were also unwilling to bear the stigma of a publicly open marriage or to go through the effort of negotiating such a complex arrangement.

These women were turning to infidelity not as a way to explore a marriage, but as a way to stay in it. Whereas conventional narratives of female infidelity so often posit the unfaithful woman as a passive party, the women I talked to seemed in control of their own transgressions. There seemed to be something new about this approach.

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In The Secret Life of the Cheating Wife: Power, Pragmatism, and Pleasure in Women's Infidelity, another book on infidelity to be published this November, the sociologist Alicia Walker elaborates on the concept of female infidelity as a subversion of traditional gender roles

To do so, she interviews 40 women who sought or participated in extramarital relationships through the Ashley Madison dating site.

Like The State of Affairs, Walker's text offers valuable insight simply by way of approaching its subject from a position of curiosity as opposed to prevention or recovery, and she investigates which factors led the women in her study to go outside their marriages.

Surely, one might think, a woman who would do such a thing must be acting out of a desire to escape a miserable marriage. And yet it turns out, this isn't always the case: Many of the women Walker interviewed were in marriages that were functional. Like the women I knew who cheated, many of the interviewees said they liked their husbands well enough. They had property together. They had friendships together. They had children that they were working together to raise.

But at the same time, they found married life incredibly dull and constraining and resented the fact that as women, they felt they consistently did a disproportionate amount of the invisible labor that went into maintaining their lifestyle.

One woman in Walker's book told her, "The inequality of it all is such an annoying factor that I am usually in a bad mood when my spouse is in my presence," and another said that while her husband was a competent adult in the world, at home he felt like "another child to clean up after."

Of course, it's a "third way" that is not feasible for everyone, even if more women are taking it up, usually, women who feel financially secure and independent enough to risk potential fallout. These women seem to be finding that no amount of sensitivity or goodwill on the part of their husbands can save them from the fact that in every arena, from work to marriage to parenthood, they're always doing more for less.

As Wade put it, "It's such a precarious balance keeping everyone happy, that for many women, to start a long conversation about her own sexual satisfaction seems like a bad idea. We now tell women that they can have it all, that they can work and have a family and deserve to be sexually satisfied. And then when having it all is miserable and overwhelming or they realize marriage isn't all it's cracked it up to be, maybe having affairs is the new plan B."

I tested this idea out on a few of the friends who had confided in me about their affairs, and most of them agreed. Twenty or thirty years ago they might have opted for divorce because surely there was another man out there who could do better in this role, who could satisfy them completely. But a lot of these women are children of divorce. They lived through the difficulties divorce can create.

"Even now," all these years later, one told me, "Do you know what my most vivid memory of Christmas is? Driving through a blizzard up I-95 in the back of one of their cars, and then they'd pull over on the side of the highway and hand off me and my brother without speaking. That was our Christmas. Why did these people marry in the first place?"

Maybe that's the essential question, the question preceding those Perel explores in her book. Why do women still marry when, if statistics are to be believed, marriage doesn't make them very happy?

I confided in a friend once that, after 15 years of marriage, the institution and the relationship itself continued to mystify me. At the time I married, marriage had felt like a panacea; it was a bond that would provide security, love, friendship, stability, and romance -- the chance to have children and nice dishes, to be introduced as someone's wife. It promised to expand my circle of family and improve my credit score, to tether me to something wholesome and give my life meaning.

Could any single relationship not fall short of such expectations? Maybe these women were on to something -- valuing their marriages for the things it could offer and outsourcing the rest, accepting the distance between the idealization and the actual thing, seeing marriage clearly for what it is and not what we're all told and promised it will be.

Many of the friends I spoke to expressed similar feelings. "I shop and cook, my husband does dishes and empties the trash," one told me. "We each do our own laundry. But I've always been in charge of the 'calendar,' and what I didn't realize until recently is that in some way I'm in charge of managing many of our relationships.

My husband is a homebody and I initiate/plan almost all of our social endeavors. My mom got this phrase from her therapist: 'keeping the pulse of the household' -- this idea that someone has to be managing the emotional heart of your tiny community. I think women do that a lot."

And as Perel repeats frequently in this book, and in her previous one, little does as much to muffle erotic desire as this kind of caretaking and enmeshment.

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"I think there's an incredible amount of deep resentment for women in America about divisions of labor," said sociologist Lisa Wade when I asked her to comment on this contradiction. "And what social scientists are finding now is that there is a correlation between equal division of labor and better sex."

No matter how much attention is paid to these issues, she told me, "these kinds of cultural beliefs hang on a long time after they're relevant. They hang on in ways that are often invisible. A lot of women have tried to address these problems and have faced a lot of stubbornness from husbands. They feel there's no way to win this battle. So maybe now what women are deciding is that infidelity is a third way."

My friend told me she felt this way of thinking was the only answer, and the way she'd come to reconcile her feelings about the relationship. She said that she used to compare her marriage to her parents', who always seemed totally in love. "Until the end of my mom's life, they were spooning together every night in a double bed ... not even a queen. But," she added, "they were awful and narcissistic, with very little to give to their children."

My friend felt she and her husband were much better parents, more involved and attuned to their kids.

"But often," she went on, "it can feel like my husband and I are running a family corporation together and that our emotional intimacy consists of gossiping about our friends and watching Game of Thrones. Sometimes I wonder if when the kids leave I should either (a) have a passionate affair or (b) find another husband. I may do neither, but it seems like (a) is more likely than (b). I don't have any illusions that marrying someone else will make me happy, not anymore."