@mediocremusicguy

Well, maybe you still felt a little bit of fondness for your ex, and possibly some sympathy at that time too, so you thought to yourself, 'Bleh, what the heck, who's gonna know?,' - not realizing that you would feel remorse afterwards. And perhaps the alcohol reduced your inhibitions as well.

If it was me, I probably wouldn't go to all the deep psychological analysis about it and I'd just simply accept that, at the end of the day, I chose(!) to cheat. Not that I ever have, mind you. And the remorse you now feel should be an emotional indicator of your inner nature as a person. Because not everyone feels remorse for cheating, going by what I can tell.

So, to me, you just chose to. But obviously you don't wish to do it again.