Love triangle, what to do?

So, my story starts 2 years ago.

I met this guy who was a bit youger than me, let's call him X, we became friends and then we started dating (sorry for my english, i'm not from america).

Everything was perfect for about 1 year, we shared a lot of great thing together (we were both virgins) but after that, things became a bit more complicated.

One time we went to a party, he got drunk, and kissed another girl, while i was in the same room. I actully forgave him because of his pleading, and swearing that he didn't remember, and that he didn't do it on purpose. From that moment i didn't trust him like i did before, and so began all the fighting.

After our second year he broke up with me, leaving me with no explanation, just an "i think you are lying to me about something, we should stay friends". For a long time i was a wreck, and we live in the same neighbourhood, and we saw each other every day. I saw him hitting on other girls, he treated me sometimes bad, but i always helped him when he needed it, i even gave him a loan.

After 6 months, on new year's, we met at the same party. I saw X kissing a girl there, so i kissed a guy. After some time i found out that this guy is my bestfriend's crush (bestfriend since 1st grade), they have slept together, and she has been bragging about him for about a year, but i haven't met him. I felt a bit awful, but i was also glad because i made X jealous. The next day he came to my door telling me that he wanted us to makeup, so i accepted.

The first 3 months were nice, but i couldn't stop thinking about the guy from the party, he called me, we chatted. On the other hand with X began the fighting all over again, sometimes it's good, sometimes it's very bad (he calls me names, etc).

Last night, i bumped into the guy from new year's, and he walked me home, and we kissed. He told me that he wanted to be with me, he knew about my bestfriend, about my boyfriend, and that he will wait for me if that is what i wanted. And now i do not know what to do. i love X but i hate the way he treats me, and i love my bestfriend, and i know she still likes him, and i care about her, and i know she will never speak with me if she found out i was with him, and i don't want to lose her.

I really like this guy and i can see he likes me. So what do you suggest?