I can't believe you are even asking. You know wtf is going on and you know wtf you should do about it.
I think the reason you posted this is because you got it bad for this chick and you're hoping that maybe just maybe someone on here might post something that will allow you to reason all this out so that you don't have to face the truth. It ain't gonna happen.
The first thing you need to do is get her purse away from her so you can dig through it and find your balls. The next thing is tell her straight up 'It's my way or the highway'.
No, don't even bother with trying to set things straight. The whole thing about her going out with her friends and not wanting you around is her way of getting time away from you so she can still act like she's single. I've got $50 that says she's screwed around on you before and got away with it. Now all she's doing is trying to make it easier to get some strange peter. She probably thinks if she can get you to puss out about her going to the movies with the new meat then she'll be able to screw around anytime she wants.
Man up ! Take her out one last time, get her liquored up, poke her in the but and dump her the next day.