People make mistakes and get caught up in the heat of the moment which is what I figure happened with the fingering on the couch. The part I have a real problem with is that after you had made it clear that you were upset and were crying in the kitchen that he was disrespectful enough to leave you there and go back to cuddling with K in your bed! Something about that just seems very very wrong. This is what I would be talking to him about. As for K, just let it go, she's going to be leaving soon. I wouldn't go out of my way to have any contact with her before she leaves either. There really isn't any point in pushing your comfort level with someone who just isn't going to be around.
Everything will be ok in the end. If it's not ok it's not the end.