As long as there has been marriage, there has been infidelity. In ancient times, most relationship lapses were blamed on the mythic seductress – the innate, uncontrollable temptress inherent in all women. In modernity, we’ve at last started to move past that sexist trope, turning to science to explain why we stray. Some studies suggest a genetic component that makes some people more likely than others to cheat on partners. Other research has identified certain personality traits associated with straying.

But these don’t fully explain the breakdown of exclusivity — of vows, in many cases — between two intimate individuals. It’s one thing to feel the yen for something different, or even feel an evolutionary urge – it’s another entirely to act on it. So why, exactly, do we cheat?

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R. is a 31-year-old professional living in Bangalore who has been having an affair for more than a decade with a married man. She herself has been in committed relationships off and on during that time. It’s an on-again, off-again continuation of a fling that started in her late teens, when he, a few years older, was getting engaged to his long-time girlfriend, now wife.

“In a decade, we’ve been together seven to eight times [for a few days each time]. And it’s never crossed our minds to stop it,” R. says. “I don’t want to call this a relationship. It’s more like a transit airport. … If he’s in the city, or I’m in the city, we meet up for a few hours. Then after that we forget that we did that. We completely put it back of our heads.”

For all her talk of ships passing in the night, their encounters have always had more meaning than mere sex.

“It started off as inquisitivity,” she says. “It was a lot of physical exploration. … here was an elder guy helping you explore your body, and it was fucking fantastic.

But over the years, I think it has changed,” R. says of their arrangement. They debate intellectually, exchange advice. They celebrated the birth of his first child together, and later, his second. They confide in each other, she says – he shares his anxiety over being the head of his family. And they look out for each other; he has urged R. to marry, calling the union a “beautiful feeling.”

Those are the only times their arrangement feels complicated, she says. “I wish that he could be this honest with his wife also. And I know he’ll never be this honest with her. I know even when he’s on his deathbed he’ll think of me. And that kind of makes me feel guilty. In this whole being unfaithful business, guilt is a constant — guilt, not for what we feel for each other. I feel very guilty toward society.”

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Society has defined romanticrelationships ever since the third human walked into the cave. Which makes any discussion of what leads us to stray incomplete without also exploring what brings us together. Intimate relationships in India, most commonly within the institution of marriage, have changed drastically over the past decade, suggests Ira Trivedi.

Trivedi is the author of India in Love: Marriage and Sexuality in the 21st Century, for which she crisscrossed the country, visiting more than a dozen town and cities to explore how mores around intimacy have changed.

“For centuries and centuries and centuries, since the beginning of time, since the beginning of societies, marriage has been all about societal responsibility, not about individuals,” she says in a 2015 TEDx talk on the topic. “Everyone got married because a church told them so, because it was a good economic arrangement, because it was a good social arrangement – that’s how marriages were done.”

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Marriage was the ultimate division of labor within society, aimed at creating a strong, but not necessarily intimate, unit: Men provided for and secured the family; women produced heirs and kept things going smoothly at home. But eventually, as industrialization has enabled labor opportunities — and thus, gender roles — to become more equal, needs have changed. Women who have joined the workforce don’t need a provider, and the demands of their work has meant that any partner is increasingly expected to divide the labor at home.

India is in the throes of this shift, Trivedi argues. As women join the workforce, as caste divisions break down, as geographic mobility frees people from being beholden to community norms, and as technology makes it easier to meet people, intimate relationships in India – marriage — have undergone a seismic shift: Unions are less and less about what society wants for us, and more and more about what we want for ourselves.

And “as there is change,” she notes in her talk, “there will also be conflict.”

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For R., as we discuss her arrangement, one word comes up again and again: safety. She knows she is safe with this man. Not from any clear and present threat, but from the judgment and punishment society wreaks on non-traditional relationships.

Without those forces, she thinks she would be drawn to polyamory, she says, her voice wavering in uncertainty. “Societal constructs are so strong in my head that even thinking about it out loud is something I haven’t really been able to do. And I’m a fairly free person. But you know the chains that you grow up with never completely free you.”

She might even be open to a not-strictly-hetero sexuality, she says — but that’s a mental leap that’s even more difficult to make. “I’ve never had a woman-on-woman experience, even though I may have gotten attracted to a woman or two in my lifetime. But it’s just that, in my head, I’m so scared of taking that step and finding out what that really is, that I prevent myself from doing things like that.”

R. says this fear is rooted in childhood internalization of what “decent” women do. No matter how “woke” she thinks she is, or tries to be, she can’t entirely shake these norms.

“I like having sex, I like not having relationships and all of those things. But how do you say that out loud?” she says. That’s where her friend comes in: He not only understood that, but respected her for it. Their secret affair is the most comfortable way for her to live her life authentically, without facing the consequences of openly flouting conventions.

“I’ve had friends who … such relations have really blown in their faces,” she says. “I didn’t want any of that. He seemed like the kind of person who would protect me. I wouldn’t have to deal with those headaches.”

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If anyone has had a front row seat to those blow ups, it’s Nisha Khanna. Infidelity is “very frequent,” says Khanna, PhD, a psychologist and marriage counselor in Delhi. “Every second case [I counsel] is of infidelity. It’s very common.”

Speaking with Khanna is a little like being in the throes of a new passion – swept along by a force beyond your ability to resist. The psychologist, armed with a PhD and 17 years of experience, speaks quickly and vividly, painting a picture of infidelity in India in broad strokes based on the thousands of couples she has worked with over the years.

What emerges from our discussion of why people seek extramarital affairs is the concept of lack — a lack of appreciation, of communication, of self-esteem; a lack of intellectual connection, of similar sexual proclivities, of alignment on expectations (especially those around gender roles) — a lack of acknowledgement, thanks to Bollywood’s roseate depictions, that marital relationships take as much work as careers.

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Of course, the circumstances have to be right, she says. Long work hours at close quarters allow for new intimacies to develop. A fight with an in-law might push someone over the edge.

But most often – 80% to 90%, she estimates — the people she works with are seeking extramarital affairs “because they have a lack of understanding for themselves,” she says, a “lack of self-awareness.” The type of top-down, controlling parenting common in India breeds insecurities, trust issues and a lack of ability to identify and cope with emotions, she explains, which carry into adulthood.

“It’s not a lack of love in these marriages,” she says. It’s that “people don’t think about what they want to do with their lives.” So, they have an extramarital affair.

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In his 1992 book, The Transformation of Intimacy, social theorist Anthony Giddens chronicles the West’s attempts to grapple with the cultural shifts that Trivedi says are current in India. He also touches on intimacy-changing scientific developments like modern contraception – all to build the argument that marriage in the 20th century transformed from a primarily economic and social arrangement into a medium of self-discovery and self-identity.

Is it possible that as our reasons for marriage have changed, so, too, have the reasons why we cheat? Where sexist myths and science have failed, societal norms might succeed in explaining why we have affairs — because they explain us.

“We are this one secret that we both have held onto for so long. That kind of control I have over this one, tiny aspect of my life, no matter what’s happening around me … it’s not just control over that aspect of my life, it’s a kind of measure stick,” R. says, searching carefully for the right words. “Here is a person that I’m completely honest to, in my body and soul. And he knows the darkest deepest things that I’ve done, which is continue a long-term relationship with him while knowing who he is, and continuing it even when I have been in relationships.”

Even if she were to get married, she says, “I think I would continue with [the affair] because, in a way, he is a mirror to who I am, who I was, and who I will be.”

And perhaps, for some of us, whom we don’t even know we want to be.