Why people cheat – and with whom – has all been uncovered, thanks to a massive survey. It was compiled into a book called The Normal Bar, which has been dubbed “the world's most extensive survey on romantic relationships.” That’s because researchers polled over 100,000 people and collecting over 1-million pieces of data. And here are some of the findings:

  • Your partner is most likely to cheat with someone you know! Not a random stranger, and not someone they picked up at a bar. 60% of infidelity occurs with a coworker. But don’t rule out the people in your social circle. Nearly half of men and a quarter of women are attracted to their partner’s friends and are tempted to act on it. The attraction – with a coworker or friend – has to do with proximity. The more you’re around someone, the more attractive they become to you, and the more opportunity you have to act on your feelings.

  • It usually happens during a business trip. Forget vacations or bachelor parties. That’s the number one scenario when are people most likely to cheat. Out of everyone who admitted to cheating, 1-out-of-3 took advantage of that setting. Experts say it happens because travelers are lonely and because business trip cheaters don’t think they’ll get caught.

  • When it comes to women and infidelity – beware of the old flame. That’s a danger zone for women – and of those who cheated on their partner, one-third fell into the arms of an old flame. That’s because women typically cheat for emotional reasons. And someone from a woman’s past is not only familiar, but there are lingering emotional ties there.

  • So, what’s the biggest reason men cheat on their partner? Boredom. That’s the overwhelming reason given by over 70% of unfaithful men – that their primary relationship has become stale and lifeless.