I've told her that I would like for her to be my girlfriend.....what should I do?

Many girls used to do this back in my day, but I think its more of a friend thing. Things going wrong with her and her boyfriend... anything would be an upgrade, but if she didn't want to be with him... she wouldn't be. She was looking for someone to listen to her and give her advice. I would move on and find you a girl without a boyfriend! :)

well dude, honestly you should just leave her be.
some girls can be teases sometimes, and those kind of girls, you don't wanna mess with.
if she's been flirting with you, she probably was having problems with her boyfriend and just wanted comfort.
and dude come on, four years!
it's going to be hard for her to leave him..
so just let her be, and move on.
there's other fish in the sea!

I understand that you really like her, and it seems she really likes you... but if she's not willing to break up with her boyfriend for you, is she worth it? (You'll probably say yes =P) It seems her relationship is unhealthy and she needs to escape it but can't. I think she feels like she's leading you on. You've got to ask her straight out if it's you or him. Seems like an ultimatum, but she's not gonna give you any answers unless you ask her - do be kind about it, but I think asking her straight out is your only hope. But be sure you don't make it seem like your'e trying to break up her current relationship...if you don't express how you're not encouraging them to break up, you might have to face her boyfriend and all his friends, who I'm sure won't be very impressed with you. Really tough situation =( I think she's gonna stay with him though. Sorry

Way to be a FRIEND.