What difference would it make whether he knows that you know or not? (Probably better if he does not if you want to proceed with D) A lying cheater already does not have a clear conscience. If you tell him that you know- most likely he will either be glad that everything is finally out in the open now, or he will turn around and place the blame on you (I know it’s crazy).
What are you going to do with this new information? Anger is a feeling....I suggest you sit with this new info for a few days until your feelings subside and can think about it with a clear mind.
