I kiased a guy who has a girlfriend..

well, I kissed this guy who has a girlfriend.. basically since I’ve started college I met this guy, but I found out he had a girlfriend. We started talking a lot and got to know each other a bit more.. this one night I invited him to a party.. he agreed to come and we met up before.. instead of going straight to the party we decided to drink before, after about 1 1/2 of being alone together we kissed.. I couldn’t help it, it was just one of those things that happened.. we eventually went to the party after about 3 hours of kissing and everyone was suspicious that something happened.. we had to tell everyone nothing happened otherwise his girlfriend would find out.. about a week later his girlfriend found out but luckily we both convinced her it was only rumours. We decided that we should still be as close as we were in college and forget about everything that had happened that night. So that’s how I thought it would be.. but we got even closer like he’d flirt with me and we’d talk about it happening again if he was single etc. Then one day after college we were just chilling and we kissed again but this time we were both sober.. it was so weird because I know he has a girlfriend and so does he.. shes always asking about me as shes really paranoid and he never tells her he’s going out with me in case she assumes something.. I feel guilty now because we’ve kissed on 3 different occasions, I don’t know what to do. I can’t help it from happening because I’m starting to really like him.. what should I do? I don’t want to be some bit on the side.. he has told me he likes me and he’s really sweet.. hes always wanting to see me and he even came out with me instead of his girlfriend! I don’t know what to do, because him and his girlfriend have been together for over a year now.. I don’t want to tell him it’s me or her because that’s stupid because he’ll probably pick her. I don’t know, I just want to know whats going on.. apparently hes been acting differently with her since we kissed maybe he is starting to lose all his feelings for her? I don’t want to be the other woman who ruins everything but I seriously know it’s wrong to carry on! ahhh, anyone been in a similar situation? if so please help!! thanksss