What would u guys think in this situation?!?!?

My ex and his girlfriend had a real bad break up recently. I guess he was needing a friend and consulted in me. We had met at Dennys to talk and I ended up getting a room and we had . He regretted what he had done and told his girlfriend. He didnt want to get back with her because of what he had done but she took him back. They are now back together and happy. He says he is going to marry her soon...what to think of this?