If you're complaining about your marriage to a sympathetic ear, you don't need a degree in psychology to know that the implicit message in these conversations is, "I'm unhappily married. Want to fool around?"
Cheating was a set of choices I made to get things I wanted -- sex, ego strokes, flattery. I didn't consider your welfare. I was staggeringly selfish. I risked your health. I risked our children's home life. All because I wanted a bit of strange.
You can argue that people reconcile out of fear, or crappy financial consequences, or keeping it together for the kids. But I also think mixed up in there is compassion -- a great big heart that is trying very hard to love someone who has grievously hurt them.