What shld i do when my friend backstab me an blame me for her issue, her goal was to use me to get her friends?

she told me we were friends! ok so i believed her and we were close...but last year she hated me, i dont know why but she did and now this year she likes me as a bff. That was werid! i lost all of my friends last year in june and she was one of them. Then apparently her and my other friend got into a fight and it was pretty bad..which made us closer! by then the other girl still hated me for something else but she wanted to make up and we did then my friend copied that idea and made up with her too? she was obvisously using me, i am so sick of liars, cheaters and bitches! i hate highschool?! well anyway time flew and we were at our dance and my freind really liked my freind ryan and they were texting nonstop it was so cute! then i see her at the dance kissing another guy and grinding him! i was so sick to my stomach... she was totally dumping him and he was so into her and she was lying! then i approach her and say "So what about ryan in jersey" and she said idont care and got pissed off becasue i accidently said it in front of the other guy and i had no idea who he was! i was proctecting my friend ryan,she is known for treating guys like ****! kinda like a tramp...or ****....im mad at her...then at school the next week i got the silent treatment and the death stare and she was mad but i had no idea who the other guy was?? then my freinds backed me up at lunch and told me to fix things so i tried and she said" Just get out of my face, i dont care anymore".....really? i was so sad--a friend i thought i had gone..then realizing she used me i refused to aplogize and give in to her slutly acts! and i was happy i did ,the 1st time i stood up for myself like that and it felt good...then i talked to ryan and i told him wat happend and he was crushed! i cant believe it and why she did it? she secretly wants back into the group but they dont want her becasue she hurt me on purpose!!!!! it looks like i got screwd againi just want to stop this drama! and B.S....now she would talk to me and is phony?? please help