I've been torturing myself over this girl for over a year?

Here is the story. I'm a sopre in High school. Last year, there was this girl I liked a lot, so I asked her out. She liked someone else, and we didn't know each other well enough, so she said no. A few weeks later, I still kind of had feelings for her, so when she started dating this other guy, I was attacked with feelings of hopelessness, as if I would never get another chance, they would be together forever, etc. After I had asked her out, I had a few extremely awkward encounters with her. One, where somebody put a note in her locker, and signed it my name. She thought I was a pervert, but at the beginning of this school year she realized it wasn't me, and she felt guilty. Then, she started waving at me, and hugging me in the halls. We started talking a lot, and kinda became friends. Feelings for her began to resurface. At this same time, she just got into another relationship. The guy goes to a different school, but he was posting Facebook status's about how much he "loves" her 7 months before they were a couple. I was immediately hit with another sense of hopelessness, and so on. I stopped talking to her, because I don't want to like her if I can't act upon it. As I watched there relationship blossom, and they become closer and closer, I've been hit with a greater sense of these feelings of hopelessness, grief, and so on. Almost like a weight on my chest, which is getting heavier and heavier. I am trying to get over her, but this semester I was transferred into her PE cl, and she was transferred into my english cl, so it has been a challenge with me seeing her everyday. I've tried to move on by completely cutting communication with her, but she now she would start talking to me, which complete destroys that plan. Last year I stopped liking her around this time because of the fact that she completely embarred me, by running away from me, due to her thinking that note was from me. I was immediately turned off. The only thing I can think of doing, is to confront her with these feelings. It would be a complete train wreck, and may break our current relationship. I don't think these feelings are fueled by my attraction to her, may be a small portion. I think a bigger part of it is the feeling that I was cheated out of a relationship, just because I wasn't of the same body type, reputation, etc. What do you think are causing these feelings, and how do I end them? I really just need it all to go away, but can't find a way.