Best way to look at this: she was attracted to you out of interest for genuine character, instead out of what is most likely terror at her brute of a boyfriend's attitude. It's not your fault if she's too weak to dump his ass, but it looks like you should keep doing what you're doing (it won't usually play out that way).

Boyfriends like that should stop and think, does this guy know she's my girlfriend

Who cares about her! Where the hell was your friends?

Well, you certainly progressed farther than I ever have, mostly because you actually hit it off with a girl, and partially because you are at least extroverted enough to set foot into a club in the first place. If I were to go to such places, I would probably not come back out alive.

That girl probably did it on purpose. There are some twisted people out there. Don't worry get out and try again. You made it that far last time you can do it again. And I can relate with anxiety. It's a tough beast to deal with. Good luck and don't give up.

the girl probably liked it, some people are messed up in the head

Mace man, there's no shame.

Gotta watch out at clubs, I knew a guy who caught a couple doing this. The chick would flirt and then the dude would beat the life out of him. This way the dude got his Inner MMA out, and the girl got free drinks. When they finished they just went to another bar. Careful.

I'm sorry it happened to you with your social anxiety.. but there are other, normal, girls out there.

I feel you, man