It happened 4 years ago. Called him out and it broke him. Still don't know what to do!

I Have been with my boyfriend for 5 years now. 4 years ago he cheated on me while I was at school. I noticed around that time he wasn't getting very sexual with me for a few weeks and acting odd and was accusing me of cheating on him for no reason. Well 5 months ago I get a call from my roommate/good friends BEST FRIEND since they were like babies telling me they had sex when I was at college 4 years ago. She decided to tell me this because she found out her best friend had sex with her boyfriend while she was in the hospital right after they had their baby (which I knew about and confirmed it for her). After receiving this information World War 3 went down. I confronted my boyfriend and he will still to this day not admit it but his reactions and emotions CLEARLY tell me other wise. I know him like the back of my hand.I have also had this confirmed with 6 other people, 2 of which are his very best friends. Since world war 3 went down, I have noticed a huge change in him towards me but also an extreme emotional change as well. He is the type of guy that DOES NOT cry. He had a very rough life and the only time I saw him cry was when his grandmother died who was the absolute world to him. Before that, when his grandfather died. I've spoken to his babies mama (who he was with for 4 years) and she also said she had never seen him cry and his friends all say the same thing. A few days after confronting him, we got into an argument about the situation and he started to cry. A few weeks later I got bitchy and brought it up again and he cried. A month ago we argued about something that had nothing to do with it and he cried (he was drunk for that part but he still never used to cry when he was drunk). I've been holding onto this and have been slowly trying to get over it but sometimes a dwell and put the guilt trip on him. If we get into any arguements (which has been ALOT less lately) and he knows he's wrong, he apologizes which is rare to admit he's wrong. Any other time he would just get mad but I FEEL LIKE I BROKE HIM!!!! He knows how against cheating I am and when I originally confronted him I told him I was DONE a thousand times but it didn't end.

I know this was a long story and quite the rant but heres what I'm really trying to say. I'm so against cheating in relationships I don't believe you can look at someone in the eyes and tell them you love them knowing you've done wrong. I can't get this out of my head and I HATE the trashy girl he cheated on me with. How do I get over it? Is it wrong that I LOVE how much closer he is with me now? Is it wrong that I brought out a side of him that hasn't existed before? I love him and I know he loves me but I just need some random opinions..

It will be easier for you, and for him if he comes out and tells the truth. I can tell that you want to forgive him, but that will be impossible unless he tells the truth. You seem like a sweet girl.
forgive him, but only if he is obviously sorry. And if he hasn't cheated on you since then, then he probably regretted it and has no intent to do it again. But remember "fool you once, shame on him. Fool you twice, shame on you." He cheats again, you have to get yourself out of there!