My ex girlfriend is going out with my best friend?

ok so in 2009-2010 i was totally in love with this girl. She didnt feel the same way and i just felt like killing myself because of how much i loved her. all my friends told me to just give up on her but i didnt. so in October 2009 i asked her out, she said she didnt want a relationship at the time and for me to ask her a little later. so ok i was giving her some time and then all of a sudden i find out that shes goin out with someone. that totally broke my heart and thats when i started really hating my life. so in december they break up and i ask her out again, but she says no and she goes out with someone else. sounds like a whore right? well it gets worse. In January 2010 i ask her out and she says yes, but i didnt really feel like it was real. everyone kept telling me that she was just goin out with me cuz she felt bad for me. So we break up like the next week. So i just gave up on her and got a new gf. then in like May I ask her out again and then we go out until like August. it was real that time and i felt it because in the time that we werent going out, we were still close friends. so anyway school started back up in september and i didnt talk to her at all but she still tried to talk to me but i just ignored and at the school dances she would always grind on me and sit on my lap but i'd just walk away cuz she made my life miserable. So i decided to be friends with her again and i found out she had a new bf. this kid kept talkin alot of trash to me on the ps3 so he came to my school wanting to fight me and i dropped him. ( i started boxing and doing jiu jitsu so i can get my anger out ) so they broke up. and like in November, my best Friend who helped me through my hard time started liking my ex. so im like whatever cuz i know that she didnt like him so ok whatever. and then at the november dance i see her grinding on him and being dirty with him and my friend thats a girl (we are now going out but we were just friends at the time) said that shes just trying to get me jealous and im like yeah ok. so around the end of Thanksgiving break, they started getting closer and im like ok theyre just friends. but then i find out that that theyre going out. I didnt really care at first cuz hes my friend and im happy for him but then he just stopped hanging out with the guys and now all he wants to do is be with her all the time and he doesnt even care about us anymore. hes always with her but then one time during lunch he was with us and im like " what happened? you cant find her?" and hes like "yeah howd you know" and i said maybe cuz ur only with us when she is absent or when she leaves school early. it really makes me mad. they dont even look good together and she is always being sexual with other guys and she is always telling him that i said things about her like i called her a slut or she says that i said things about him. She is the reason im not friends with alot of people that i used to be friends with. If you read this to the end then thank you and pleasse help me. what should i do? he was a really close friend and now i don't really hang out with anyone anymore because we had our own group but now that he doesnt hang out with me anymore, its not the same. please help