Leaving someone for someone else: what the studies say

The idea behind the saying is that the new person isn't the cause of the breakup, only the trigger. The real reason would be what wasn't working before: distance creeping in, the arguments, or a desire that had faded.

And it's often the case. A study published in 2018 asked people who were thinking about leaving their partner what was pushing them to go. Among the reasons that came up most: broken trust, things about the partner that had become hard to live with, and a partner who was slowly pulling away. Nearly one person in two also had reasons to stay. When someone has been on the fence like that for months, meeting someone new is enough to tip the scales.

But the saying doesn't tell the whole story. American psychologist Shirley Glass, who studied infidelity for decades, found that 56% of men and 34% of women who had an affair described their marriage as happy. So people can also leave, or cheat, when things were going fairly well: out of attraction or a need for something new, or simply because they met someone at the wrong time.

That's the other saying you hear a lot, and it doesn't hold up well against the numbers.

First, it isn't mostly men who leave. Stanford sociologist Michael Rosenfeld followed more than 2,000 American adults between 2009 and 2015: women initiated 69% of divorces. Among unmarried couples, men and women ended relationships about as often as each other.

Second, there is a real difference, but it comes after the breakup: men get into a new relationship faster. In France, among people who separated between the ages of 25 and 50, 55% of men had a new partner within five years, compared with 45% of women, according to the national statistics institute (INSEE). When an ex starts a new life within a few months, it's tempting to conclude that's why they left... when sometimes the new relationship only started afterwards.

Finally, men and women don't experience an affair the same way, on average. Shirley Glass noticed that men's affairs were more often sexual, and women's more often emotional, and that women who had an affair were more likely to say they were unhappy in their marriage. So when a woman leaves for someone else, the relationship had more often been going badly for a while.

A breakup always hurts. When there's someone else involved, another kind of pain gets added: comparison. You wonder what the new person has that you don't, and you end up looking for what's wrong with you while scrolling through their photos.

That comparison leads nowhere. The new person mostly showed up at a specific moment, often the one when your ex was already looking for a way out. And checking their profile every night doesn't help: a 2012 study of 464 people found that the more you look at your ex's profile, the more you suffer from the breakup.

There are also the reasons people give for their own divorce. In a large American survey, infidelity was the reason mentioned most often, ahead of incompatibility. But the same people were far more likely to blame their ex (33%) than themselves (5%): everyone tells the end of the story from where they stand, and the third person makes an easy culprit.

• Cut contact, at least for a while: no texts, no "I just wanted to see how you're doing". Every exchange restarts the waiting.
• Stop following their accounts: muting or unfollowing protects you, even if it feels childish.
• Don't look for someone to blame: not you, not the new person. Your ex made a choice, and that choice is theirs.
• Talk about it: to friends, to family, to a therapist if the pain lasts. Keeping it to yourself makes it go round in circles.
• Be careful what you conclude about yourself: "I'm not good enough" is a thought that comes up a lot after this kind of breakup. It says nothing about you, though.

It happens. A relationship that started in the turmoil of a breakup, or while the previous one was still going, can run out of steam once the novelty wears off. But there's nothing automatic about it, and waiting for that moment can keep you stuck for months.

What matters most is what happens after the breakup: whether you're still talking, whether the new relationship gets serious, whether your ex expresses regrets. A new relationship that lasts, with moving in together or plans, greatly lowers the chances of a comeback.

And if a comeback ever comes along, ask yourself what would have changed. Going back to someone who left for another person means rebuilding trust, and that doesn't happen in one evening.