What do i do?

so.. back last year i dated this girl for a really fucking long time, like a year or more of something like that, and we stopped going out like 6 months ago, and it was helllla awkward at first when we would see each other, and we hang out with all the same kids, and then it was alright for a bit.. but after we stopped hanging out she sort of turned into a bitch, and starting talk shit and just totally being blehh for no fucking reason, and wanting nothing to do with me. which i was / am don't really give a fuck, because we just started to kick it with different people, so i never really had to deal with it.
but now, since its the beginning of the year everybody is hanging out all together again, and shes always around, and is always bitching about me behind my back, or jsut being hella stupid (and she totally hates on skiing, all the fucking time.. gay) and i have to deal with her just acting like a dyke whenever shes around me.

okay, epic rant above ^ but the problem is that since shes friends with all my friends, she's always inviting them to her house and they all party there and shit, it hasn't happened that many times, but when it does it totally sucks, and she never wants me to come to any of this and just plans all this shit in front of me. and then they all go party and i end up jsut kinda doing nothing.

my question is: what do i do to either get her to not hate me? or figure out a way to make my shit work out when she invites all my friends to party at her house without me?