Girls: What Do I Do!?

Alright, so theres this girl. Known her for 3 years, and for a while, Ive realized that she's the girl I want to be with. Now, I know for sure Im not foolishy blind and infatuated with her. Theres kinda the issue that she has a boyfriend. I dont know if maybe I was afraid that Id just be some fling (yeah, i got dumped because i was just some girl's "fling") or maybe I wanted to wait. Anyways, I let her slip thru my fingers, and I dont want to do it again. Ill be day dreaming about her in science, and Ill see her lookin at me, then I look over, and I stare into her eyes for a brief moment, then I look away. I get erflies when she and i do that. And out of all the guys, she'll ask me for help. Idk, maybe because I know everything. But should I wait for her, somehow get over her, and move on?