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?"
It's hard to imagine, but even if you never fully forgive your cheating spouse, your feelings of anger will likely soften over time. It would be tragic if you sent a destructive message now that you couldn't take back later.
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.
All those other transgressions seem to pale in comparison (yes EVEN the "you are your mother" comment) to stepping outside our marriage, our union, the lives we've built, the unit we've created as a couple and sharing himself in the most intimate way with another person.