This sounds sort of familiar... my gf and I started off with kind of a weird relationship with me liking her and her liking me as a friend, and her liking this other guy, and him not really liking her, but hooking up with her periodically which raised false hopes in her, which then crushed my hopes, which had been rising... and so on. Long story short, we're engaged now.
I stuck with it, and now we're very happy together, but there were times in the beginning when I almost broke it off with her. I even wrote out an email, detailing my reasons, but I never sent it, because I'd had a huge crush on this girl for years, and now I was so close to making it work, and I really wanted it to. The first time I told her I loved her, she didn't really say anything back, kind of like in the Seinfeld episode ("Huge matzah ball"), but eventually, I won her over.
My advice to you would be just to let it play out, and it will eventually resolve itself. I know from personal experience how hard that can be, and how agonizingly painful it is at times, but I also know that the rewards can be incredible.
I think dirtboy is right, though, if you can't truly be her friend, then don't be her friend. But by God, be the best damn friend you can be, and maybe you can eventually convince her that *she* loves *you*. If you are always there for her, and always willing to listen, to talk and to care, then you'll basically be putting the ball in her court, and it will be up to her to decide. Think of it as playing defense, I realize it sounds more like playing offense, but if you think about it, it's not, you've made your move, it's her turn.
Good luck, Ruroni.