We kissed BUT he has a girlfriend... What to do?

I know, I know, I get it, I'm a whore, but this is NOT the kind of person I am. I never done anything like this in my life. I grew really close to this guy at my school since we are in a play together and at first I just saw him as a friend. He would hug me and kiss me on my forehead and hair, but I just thought it was him being friendly. Then a couple weeks ago he just got more touchy with me and he calls me sexy, adorable, hot and pretty. One day he kept hugging me from behind and kissing me on my neck and cheek and occasionally touching my butt. Two days later we kissed and it was my first kiss. Later on we talked about it and he told me he was sorry and that he just made things more complicated for us.

He told me that he was crushing on me but that he was trying to keep it from getting out of hand so as not to hurt anyone. He never said he regretted the kiss to me and I don't think he does. He also told me that if he'd never met his gf he could see us as a really great couple.

I know that he loves her and I'm okay with that but two days ago I was sitting on his lap and just had my arms around his neck and leaned my head in the crook of his neck and he kept kissing my cheek and hair and then we kind of looked into each others eyes and were about to kiss but stopped ourselves.

I don't know what to do. I know it's wrong to be doing these things with a guy who's taken but (and I am NOT justifying my behavior) it makes things even harder to say no or stop because of the fact that I don't know/am friends with his girlfriend. I've seen pictures of her and he's told me problems he's had with her but nothing more. They have been together for 2 years on and off. She's cheated on him before and they were just recently on a break but we've been doing these things at the time that they got back together. I don't know what to do. I'm not looking to be in a relationship, but I don't really want to stop what we are doing.

What do y'all think?
We kissed BUT he has a girlfriend... What to do?
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