You, my friend, are in the friend zone. I have to say give up now. You either are (a) going to do nothing about it, and fit nicely into the non-threatening-friend space, or (b) attempt to wedge yourself between her and her boyfriend, which makes you an asshole. And not the asshole that girls like, but an asshole that girls hate.
If you feel that your feelings for her are turning you into an obsessive creep, best to tell her how you feel, and then understand (when she tells you that she sees you as a friend), that nothing will ever happen between the two, and lay the matter to rest. I actually did this this morning. It was not as painful as I thought it would be.