Lockjaw

PSYCHO!!! Trust me man give this one a wide birth. She's a tease,she's wishy washy, she sounds immature...but then again I doubt you are trying to marry her.
She has you all twisted up and she knows it. She's just holding you in her back pocket just in case the guy she'd rather be with falls through. The mere fact that she is willingly staying in a relationship with a person that is all those things she listed and those are the reasons she CAN'T break up with him instead of it being a bonafide reason to dump his butt further in my book proves this chick ain't worth the time.
To me it sounds more like you REALLY want to lose your virginity than this girl being somebody that you really and truly want to be with relationship wise. So I'd suggest taking a long good HONEST look at your desire for this girl and if it's more for the booty...then you might want to reconsider how much that is really worth.
But I know what it's like being an 18 year old that wants something so badly that they are willing to put up with so much shit it's not even funny.
Here's what YOU need to do.

Put your position out there. Tell her how you feel stop pussyfooting around and just put it out there. You don't need to give her an ultimatum of dumping her boyfriend she SHOULD be bright enough to figure that out on her own but you need to make it clear how you feel in no uncertain terms. Then leave it at that.
She likely will bite because it sounds like she is looking for a stronger male than the one she has she's just not sure you are that alpha male yet and frankly you haven't acted like it as most guys would have jumped on her the second she made that initial statement and would have said screw her boyfriend and persued her until she said yes or wouldn't talk to you anymore.
If in two weeks she still hasn't dropped her loser boyfriend then you need to start making yourself a little bit more unavailable both emotionally and physically.
In my honest opinion this chick is using you as an emotional dumping ground or she WILL be using you for this at some point. You just need to make that call of if she's worth it. One thing though this should give you a reason to be more confident around the fairer sex and be willing to take risks. It should be obvious by now that you do at least bare some attraction to the females so use what you've got. Just be confident.