You clearly need another kick in the head, Kit Kat. A harder one this time.
You think you wouldn't "allow" him to cheat if he were yours. That is laughable. You wouldn't know he was cheating, dumbass, just like his girlfriend doesn't know he was cheating, just like the fact that YOU don't know about his new girl, probably another "friend" of his girlfriend's, who he is pursuing now.
Oh, does that surprise you? The fact that he might be leaving you alone now because he's found someone who is more willing to give him that blowjob in the dark alleyway you were alluding to?
Yes, he's a douchebag and you are a terrible friend and a bad person. Stop defending what you've done. If your friends knew, they'd dump you flat and you know it.