My Conundrum

I haven't been posting lately because my mind has been so preoccupied with this problem. In fact, I have a conundrum. So I've been casually seeing this friend of mine, on/off, for about 7 months now. I liked him but I wasn't interested in pursuing a relationship with him after my Big Breakup. We're still "seeing each other casually" but the situation is more complicated. I would love to be his girlfriend now but I can't. And here are FIVE reasons as to why I cannot.

1. I made a promise to myself in the 11th grade that I would only have one more boyfriend.
And Lo and Behold! my Big Ex was my third boyfriend. We dated for almost a year before I completely destroyed the relationship. I just feel like it wouldn't be right.

2. He doesn't like me now as much as he did before.
He doesn't really hate me but I can tell things are different now. Last semester he used to come up to my room just to hang out with me. This year, everything is different. He almost never comes to my room. When he does, it's because he wants to talk to one of my suite mates and not me. I can honestly say he treats every one of his female friends better than he does me. He's not flirting with them. He's honestly just nicer to them. If there's something funny on his phone, he'll show it to them and ignore me. If he finds something cool or if he can do something cool, he show them how to do it. I'd have to ask for his attention. And if I do he'll hit me with his signature catch phrase "Shut up woman!" I really can't deal with that. Speaking of which...

3. He always insults me now.
I swear he treats everyone better than he does me. In the Caf, our school cafeteria, I am the butt of all his jokes. He will never say anything if the others are joking about me. In fact, he'll join in. And don't get me started on how many compliments I get from him. The number is probably ranges from 0-1. And whenever we're alone it's just quiet, or he's insulting me. You'd think he'd be nicer to me when we're in private right. Wrong! I told him off about it but he really does not think that he's not nice to me. Everyone can see this but he can't.

4. I don't know how to be in a relationship.
Like what do I do? What if we want to break up? What if the ex that he worships comes back to the school? Like what do we do then? What if I make the same mistake that I did with my ex. He'd kill me. I don't want to risk that. You know what they say, 'Once a cheater always a cheater...'

5. It won't be fair if we get together.
Last night he got super drunk and he was yelling at me. He's was saying stuff like it's not fair that when he liked me, whatever he did wasn't good enough and now that I like him it's magically enough. He also said that he doesn't like being the second choice just because that the guy I used to like isn't here this semester and now he gets a chance.

I put point 5 in there because I'm not the sole victim. I just don't know what my next move should be.