Forgiving does not mean you have to stick around...
Forgiving will make you feel better, but it's not the same as letting him get away with what he did just like that. You can let go of your anger and resentment, and still realize that you don't want to share your life with someone who betrayed you like that.
You have all the right to want to be with someone who loves you, honors his marriage vows, and doesn't stray. Even if you stay mad at him, he committed the greater sin. You have nothing to feel bad about.
Not if they *puts on sunglasses* COSINE a polygamy document with you.
Ba dum tss.
bad math joke there...
The "sin" is in the cheating...
if you can't forgive another, God won't forgive you
Sin is everything that separates us from being like God, and God forgives the cheating spouse if they stop cheating and are truly sorry; they repent.