I regard cheating on one's spouse (or in any committed relationship) as one of the less forgivable sins. It destroys trust, sometimes to the point that it can never be rebuilt. In the few cases where the wronged party is indeed willing to forgive and rebuild the relationship, it can be overcome; but in my experience as a former pastor they're the exception rather than the rule. I also prefer to try to resolve the situation as peacefully as possible, with as much mutual respect as possible, for the sake of both parties in the future.
Nevertheless, sometimes one side decides to throw gasoline on the flames instead of water. One such epic occasion has just come to my attention, and even though I can't approve, I had to laugh out loud reading it.
“So I know something is up and after finding a bottle of champagne and two glasses hidden in my closet something in me snaps. So I do what any sensible man would have done. I leave and go to my friends house pretending like I am going out of town. While there I call up her mother, father, sister and several of her friends. I tell them how I want to give her a big surprise by sneaking into our room with party streamers, kazoos and a big cake with candles. Sounds fun, right?! Well, boy was it.”
There's more at the link. Go read, and (hopefully) give thanks no-one's ever done that to you!