Dont know what to do...help?

ive liked my best guy friend for a long time. &this year i started middle school&made a lot of new friends. every weekend me&him hangout. bt i made this new friend tht i became really close to. i told her i liked him a lot. then like a week later he decided he liked her&she went out with him. and they broke up. and they went out again&broke up. i wasnt really mad tht she went out with him (even though every1 thinks it was so nasty) bt she always rubs it in my face&stuff&hugs him and shes being so nasty about the whole thing. it got so bad tht i de activated my facebook&stopped hanging out&talking to her. i cnt even sleep this is bothering me so much. &she dosnt have a lot of other friends bc she kinda lies alot. &she keeps writing stuff of facebook&formspring bout how horrible her life is cause every1 is mad at her. &now the guy i like is getting mad at me for doing this to her? he wants me to jst be her friend &get over it. bt he dosnt get how she makes me feel. and she treats him so bad! she like hits him&stuff! she makes fun of him&steals his phone. i tell her to stop all the time, bc it really bothers me to see tht. she even admitted i liked him more &she does tht. and he still likes her! &whenever i say something to him about it he says "im used to it". if i was going out with him i would treat him so good! ugh.honestly i want him to like me, bt i want him to be happy. shes so mean to him& he knows i lke him&idt he really cares. idk wht to do about this whole thing. omg im so lost