and I really do not know what to do.

Him and his girlfriend were dating for two years and they broke up. A while after this, my friends introduced us and we got to talking and ended up texting and talking, and we hung out as friends with a few other people two. I really liked him and decided to maybe try to go for him.
The he went to a concert and called me during all the sweet songs and stuff so i could listen with him, and even tried to talk to me between the songs, it was awesume.

Then we were flirting the next day as we usually did, and he suddenly came out with he was back with her. I told him to go away, and stop flirting with me when he has a girlfriend, because I felt wrong and didnt like it when he was taken. He said he understood and would stop flirting with me. Then i forgot for a moment and I flirted with him. And then I kept flirting until he flirted back and I remember and was like oh crap. I asked him why he got back with her, and he said that it was because he was drunk and afraid that she was going to do something really bad to herself so to stop her he agreed to get back with her.

It was then the weekend after my birthday and he said he was coming down to newcastle with a friend and said that i shoulld go out and meet him too. So me and my friends went out, as we had originally planned to, and me and him ended up kissing. And people kept coming up to us telling us we weere such a cute couple and go so perfect together, and we were like o.o what?

We have have kind of had a few dates... and and I asked him what was going on, like between us. and he said " I really really really really really really like you alot, and me and that are over just not offically, but it should be offical by this weekend i hope if everything goes right."

It is the weekend now, they are still currently together, and i feel incredibly guiltty. like i have moments when i completly hate myself for what im doing, but he makes me happy, he treats me like im the best most precious thing in the world. he always is asking when he can next come down, and when i said i would go up to see him he refused saying that he would come down here. (not because his g/f would be about there, me and him have hung out their a few times, its where we usually meet)
he wants to read my stories and stuff, and asks about my hobbies and what all i do and basically everything about me. he treats me better than anyone has ever really treated me.
i do not know what to do. i think he feel guilty about having to break up with her twice in a row and is also worried about how she will take it, but i cant live like this just waiting for her to be gone, i cant live doing this and feeling all this guilt. i feel so horrible! but at the same time he makes me smile.

worst part - i chose to get involved, and now im lost and feel like crap.

does anyone have any advise? what should I maybe do?