Something bad happens, and you realize that maybe this act was a sign that your relationship was already kind of over; maybe you just sadly needed something concrete like cheating to come to the realization. However, that definitely doesn’t justify cheating, and it doesn’t make what happened okay. With that mindset, you can forgive the bastard because I’m sure he’s feeling awfully guilty and has tried ever so hard to get you back through chocolate, flowers, and other tokens of love that come in edible or aesthetically pleasing arrangements.
However, you’ll realize that it’s probably best to just forgive him and let him move on, and hopefully you can do the same. However, it’s going to be tough to ever forget the feeling of betrayal, and there will be a lasting effect, maybe subtle hesitations in future relationships, too. “Sorry new boyfriend, I’m broken. Blame my cheating ex and fix me.”