The man cheated on his wife. Of course he's a dishonest coward. What did you expect? If somebody acts disreputably in one relationship, they'll usually do it in the next one as well.
I haven't really taken revenge on anyone. Unless you count saying really mean things or trying to guilt trip a person I was mad at. Even then, I usually just ended up feeling bad and liking myself less afterward. It's not worth it.
Just consider this a lesson learned in getting involved with a taken man and move on.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy