Alright, I can see you're emotional and kind of a trainwreck so I apologize for calling you rapey. And for calling you a trainwreck.
Affixing yourself to this girl is not going to help your insecurities and self-confidence problems. The only reason you're hanging on so tightly to this girl is because you've got no one else and you're too afraid to meet new girls. You've found the one girl that will tolerate your issues so you're "in love" with her. This is a terrible thing to build a relationship on. Your neediness and desperation will kill any attraction a female might have for you. And I can say with some certainty that this girl doesn't view you as potential boyfriend material. Oh wait, I just re-read and saw that she herself has told you it's not going to happen. Plus she has a boyfriend.
It's really not that complicated. You need to stop this. Please just acknowledge that there's something wrong with the way you view her, and then make steps to right it. Okay?