It’s An Ugly Truth: The 8 Most Common Reasons People Cheat
They want to be “new” again
Many people are addicted to being “new” to somebody. They like being mysterious, and having a person crave knowing more about them. But they like to keep a person in that state of craving. And obviously, as relationships progress, you can’t remain mysterious forever, or else you wouldn’t be able to get emotionally close. So, as soon as the mystery goes away for some people, so does the fidelity.