Dude, you got it bad.
My $.02 (if it even matters):
She sounds like she is keeping you on the back burner and enjoying the attention you're giving her.
Find another (single) girl to take your interest.
Of course, this is the correct and logical response, but in matters of the heart, what good is that?
While the French Foreign Legion might seem outdated, the United States Marine Corps offers a three month course of therapy, followed by year long tours of exotic locations, that makes most young men come to revile the thought of the young lady whose charms prompted the spur-of-the-moment enlistment.
YMMV, of course.
If you really want to draw her in, cut her loose and start ignoring her.
She's craving your attention, and once it's gone she'll be chasing YOU for a change.
Sounds crazy, right? It works. These are just the games the young women play. If you're gonna play, know the rules.
+1 to each of these.......well.......almost each of these.
I would have a hard time becoming the back up; the guy she knows will always be there.
Oh, she's not. She has guys coming onto her all the time but she behaves.
It's funny... neither of us is actually open to the hook-up thing o_o I'm playing for keeps and she's not going to go screwing around behind her guy's back. This is... a very misplaced scene for a bar.
I like that you seem to have a strong set of morals in you. Whatever happens, don't compromise that.
I think you should invite her somewhere to have a chat with her and understand what's going on. Try a restaurant where you will actually be able to have a conversation without shouting. A Cafe is usually great too.
This sounds like good logic. The easiest way to find out what she's thinking is to ask her. Don't assume.....never assume!