It's been a long time but I saw your post and thought I'd check in on you.
My advice is not to tell him what you know. It gives you more power to have this knowledge to yourself right now.
Ask yourself what is to be gained by telling him. Of course you WANT for him to tell you something reassuring, but honestly, will it matter what he says? He will be put on the defensive. He may lie to you. He will feel intruded upon.
Right now he feels guilty and he is going to work a little harder for you to trust him. Once you show him he is the bad guy again, he will lose his desire to make up.
I say keep it under your hat for now. See how things play out. If he is seeing ow woman again, you won't be able to stop it by confronting him with it.
Do keep your eyes open though. Absolutely take him up on the offer to go off for a weekend! Let yourself have fun and enjoy each other's company. Let him see YOU are the woman for him.
Breaking it off with the ow is hard and can take a while and who knows--she may be trying to beg him to go back and he is spending time trying to tell her it won't work. Who knows, but for now, you have the knowledge which, is power and if you ever need to, you can use it.
Sorry you're going through this, it must be tough.
