Alright, sit tight. Cause it's a LONG story. I'll try to sum it up as much as I can.

Okay. So, I have a best friend who I ended up liking somewhere after Christmas. Him and I hung out A LOT and we talked a lot, just as best friends do. I ended up developing feelings for him, but I didn't want to admit them because I didn't want to ruin our friendship. But, apparently he liked me that entire time I liked him. He finally told me that he liked me, right after he got a girlfriend. >:/
After thinking about if I actually did like him back or not, I told him that I did. But, I didn't really want to get into a relationship with him because of the whole reason of not messing up our friendship.
He understood, which was good. So, i just told him to stay with his girlfriend and be happy, because all I really want for him is to be happy.
A month goes by, he's in this whole situation on if he wants to be with his current girlfriend or me. He's already told me that he "loves" me, and that he wants to be with me, but he doesn't want to hurt his girlfriend because she has already said "I love you" to him(which I'm pretty sure he has said it back to he as well).
Anyways, over a vacation from school, he asked me if I wanted to hang out with him. I told him sure, so the next day he came over my house. He told me he was on break with his girlfriend, and that he wanted to kiss me. I told him about 10,000 times before that I didn't want to be the girl that he cheated on his girlfriend with. But, he insisted that it wasn't cheating. I did want to kiss him, but then I didn't- because of the whole cheating thing.
He then caught me off guard at one point and kissed me, and I couldn't help but kiss him back. For the entire night we just couldn't get enough of each other. (Don't let your minds get carried away, we only kissed and made out. Haha.)
The next day at school, I thought things would be different. Where he would actually show me some sort of affection in school, now that me and him kind of had a thing going on. But, no. Nothing happened. He seemed to be avoiding me more than actually trying to get close to me. I confronted him about this that night on the phone, and he told me that all he was was on a break with his girlfriend and that he was more than likely going to get back with her.
Now, this- got me EXTREMELY mad.
What gives him the right to be all over me, then end up going back with his girlfriend? It got me very, very angry.
The next day, I didn't go to school. I was way too annoyed with everybody and everything.
He then got home after school that day, IMed me, and he knew I was mad. Apparently, from what he says, I told him I wasn't going to be mad if he got back with her. Which was clearly a lie, because I don't remember saying I wasn't going to be mad, ever.
The next day at school, both of us couldn't even look at each other. We were so angry at each other it was unbelievable. But, he was only mad because I had a perfectly legitiment reason to actually be mad, and he didn't.
But, I couldn't handle having my best friend being mad at me for the entire day and weekend(this happened on Friday.), so I apologized to him after school.
Yeah, I was the one who apologized for his wrong-doing. I told him I was sorry. I told him I didn't want him mad at me.
I told him that I knew as soon as we started to like each other, that everything was going to be ruined. He ended up telling me that it's not ruined. It only seems like it is because of the way I've been acting.
Which I don't understand, because the way I've been acting has been the way I normally act with my close guy friends.
I get jealous of other girls, what girl in the world DOESN'T get jealous over other girls? >:/ Ugh.

He's just so confusing and he basically used me, and now he's just going to get back with his girlfriend.
I don't know what to do! Please help!

I completely understand what you're saying. But, the only thing is, that I do want to be with him. Him, his girlfriend, and I are all stuck in this little love triangle.
His girlfriend doesn't have a clue at all about me and him though. Which makes me feel bad for her, because she doesn't know what her boyfriend had done behind her back. Even if they were on break, she should still know. In my opinion, she should have the right to know. But, of course he wouldn't tell her, if I was him- I'd tell her out of respect.
But, anyways. I do understand what you're getting at.
There is a little more to the story, but I don't really know how to explain it;
other than that him and I now tend to fight a lot more ever since him and I confessed our feelings towards each other. The fights arn't ever about a relationship problem or our whole situation that we're in, but it's more about how much, apparently, I screw up. I get blamed for most of the things that we get into fights over, he never seems to take part of the blame, although he insists that he thinks about other's feelings before his own.
I guess I just don't know what to do at all. I try to be nice about everything, I just told him to be happy with her, and just get on with his life. I'm fine with being his best friend and he's fine with being mine, but it doesn't take away from what he says to me all the time. It's like; he can go and date who ever he wants to, but as soon as I develope an interest in a boy- he goes crazy and tells me that he's probably going to end up fighting the kid.
He's sooo complicated.