One evening in Moscow, Tanya (not her real name) found herself at a dinner table with a group of friends, most of them married couples. One of the men started to tell a story about the coda to a recent guys’ night out. He’d stumbled home the next morning to his wife and two children—a 2-year-old and an infant—to find that he’d forgotten his underwear. Everyone at the dinner table, including the man’s wife, laughed at the story: the hijinks!

Wandering spouses have become a common trope for the women of Moscow. “Men’s environment here pushes them towards cheating,” Tanya told me, adding that, these days, a boys’ night out in Russia often involves prostitutes. Tanya and her friends are young, educated, upper-middle-class Muscovites, but talk to any woman in Moscow, and, regardless of age, education, or income level, she’ll have a story of anything from petty infidelity to a parallel family that has existed for decades. Infidelity in Moscow has become “a way of life,” as another friend of mine put it—accepted and even expected.

This is quite a shift, given that 20 years ago an affair was considered a career-wrecking scandal. But by 1998, a study showed that Russian men and women led their peers in 24 other countries in their willingness to engage in and approve of extramarital affairs. Since then, these attitudes have taken hold more deeply after a prolonged consumer boom that encourages Russians to indulge their whims and desires. What does this culture of infidelity look like, and what are the costs?

Any explanation begins with a basic cultural difference. When Christianity arrived here, in the 10th century, it landed in a peasant, agrarian culture that treated sex as a natural barnyard phenomenon. Russia’s expanse was notoriously hard for the already disorganized church to govern, and so, when it came to sex, a sort of dichotomy of word and deed persisted well into the 19th century, more than in the West. Then came the Bolshevik Revolution, which rooted out the church and replaced it with a prudish, asexual model for behavior. Sex, once viewed as natural if vaguely sinful, ceased to exist altogether: “There is no sex in the Soviet Union,” the saying went. Parents stopped having the birds-and-bees talk with their children, and men could be dragged in front of their local Party Committee or labor union and made to suffer professionally for infidelity.

But this was not a deeply entrenched new morality; it was a code of behavior that did not convincingly explain itself. Communist ideology—a political and economic view of the world—was not a good stand-in either. Why was sex a taboo topic for socialist citizens? Why was cheating on your wife amoral if Communism rejected traditional bourgeois norms? The Soviets answered only with prohibitions and contradictory rhetoric. Outwardly, the prudishness held into the late Soviet era: Sex remained a shameful, tasteless topic, and it was impossible for girls to buy condoms in stores. (This was when abortion was the most common form of birth control.) At the same time, studies showed that Soviets were having sex earlier, getting married later, and doing all the other things their Western, sexually liberated counterparts were doing, but without the debate to make sense of it. It was, once again, a new set of behaviors devoid of moral explanation.

This was the perfectly explosive mix that greeted the overnight arrival of market capitalism and the oil boom of the last decade. Suddenly, there was no one to forbid anything or to admonish anyone. Everything that could be had, was; one needed only the will to acquire it. All of this has thrown Moscow into a consumer-driven hedonism that would make an American mall rat blush. Everything is available and everything is for sale. Sex is just another pleasure product, like a bottle of Moet. A recent Russian movie, What Men Talk About, featured four middle-age men on a road trip discussing the burdens of married life and the pleasures—the necessity, even—of infidelity. “Why can’t she understand that sex with my beloved, and sex with some other woman are two completely different activities,” one of the men says, comparing the latter to sneaking baloney from the fridge in the middle of the night. The film was, of course, a hit.

As the movie showed, the liberation is more for men than for women. For all its modernity, Moscow has been the seat of resurgent Russian paternalism since the arrival of Putin and his conservative nationalist agenda. Since men are the ones carving up the pie and doling out the slices, the way to show you have lots of pie is to be able to afford (wine and dine, regale with gifts) more than one woman. A 30-year-old Muscovite named Lena told me that certain social circles don’t accept her male banker friends if they don’t have mistresses. “It’s like having a Mercedes E Class,” Lena explained. “If you can’t measure up, if you can’t afford it, you aren’t welcomed. It’s easier, I guess, when you have common interests.” One middle-aged Muscovite who runs a successful business recently told me, “I don’t know, maybe I’m a complete fool for not having a mistress like everyone else.”

For the most part, Russian women shrug off the fooling around. It’s seen as unavoidable and natural. Men are slaves to hormones. Why get worked up over that, or the weather? “My sister’s husband cheats on her,” says Tanya, of the underwear story. “She knows this for a fact, but she doesn’t cheat on him. When I ask her why she stays with him she says, ‘I’m going to split up with him over some nonsense? He’ll get it out of his system and settle down.’” “Faithfulness in marriage is seen as something that is nice but unrealistic,” says Moscow sociologist Irina Tartakovskaya. She points out that if women don’t really expect it of their husbands, they can pre-empt feelings of shock and betrayal.

Women also put up with infidelity because there are simply more of them. Since World War II, when the Soviets lost 27 million people, there have been real or perceived shortages of men in Russia, who have one of the lowest life expectancies in the developed and developing worlds—age 62, compared with 78 in the United States. There are nearly 10 percent fewer men than women here between the ages of 15 and 64. In the aftermath of World War II, a single man could father children with multiple women because it was the only way for many women to start families. Sixty-five years later, even perfectly sculpted Russian women talk about the fierce competition for a mate. (This is also how they explain why they are always dressed to the nines.) “Men are not afraid to lose their women here,” a 23-year-old Muscovite named Olga told me. “But for a woman, who the hell knows if you’ll ever find another one?” This recalls a Billie Holiday-esque traditional Russian women’s saying, “He may be bad, but he’s mine.”

Accepting infidelity doesn’t neutralize the harm it can do, however. Three of my Russian girlfriends, all attractive women under 30, are caught up in the attendant misery. One friend has a boyfriend who has lived with her but vacationed with his wife and kids for years. When she first found out he was married, he proposed divorcing his wife and marrying her. He didn’t do it. When she brought up the subject, he said he’d been joking. Years later, she has given up on kicking him out or fighting with him. “I don’t even know what I want anymore,” she told me. Another friend dated a man for months who said he was single. When she discovered he was married, he too said he’d get a divorce. This time, the guy meant it, but my friend soon found out that he was getting remarried in two days’ time to a different woman. She went on seeing him for months, including on his wedding night. I have my own tale: I was once propositioned by a newlywed man with a 6-month-old child. When I protested that I was not a home wrecker, he reassured me that his home wouldn’t be wrecked, whatever we did together. (I refused.)

Tanya, for her part, couldn’t take the knowledge that her husband was cheating on her. She divorced him even though she is 30 and has a child, which makes a woman essentially unmarriageable in Russia. Lena has taken a more subtle and typical approach. She’d asked her boyfriend at the start of their relationship if he had other women. He’d said no and ardently pursued her. Then she found out he was married and had two children. Instead of breaking up with him, though, Lena decided to “turn the tables,” as she puts it, by holding him at arm’s length but not cutting him off entirely. “There is a reason I’m having this experience, and I will obviously be able to learn from it,” Lena says. “So I have decided that I am not his lover. He is my lover.” He still talks about marrying her. When he does, she just shows him where she has changed his name in her phone to “Traitor.”

Like Slate on Facebook. Follow us on Twitter.