Ok, first off, regarding the self doubt; one of my favourite quotes from House M.D. is "how's self doubt going to help you when you're right?".
For the most part, things have never really gone my way either, but I'm pretty much just coming out of a long period of depression, and it wasn't that long ago that I was in school, so I can pretty much relate to your situation.
summerof2010's suggestion of just fooling around with someone is a terrible idea (not that I've done it myself, so I'm not talking from experience here). Firstly, it would probably be very unfair to whoever it would be. Secondly, it would be clear that you wouldn't really want it, even if only to yourself, because you'd rather be with the girl you said tore you a new one. Regarding the love aspect of your depression; it took me a long time to learn that there's so much more in life than love, and that love is only part of an entirety. Also, based on what you've said, it seems fairly clear that she's, at least currently, not a great person. It's quite likely that, since she likes the biggest douchebag there, she won't really be a great person for a while. Maybe I'm wrong about that, though.
Regarding public humiliation, you pretty much just have to hang around with friends in a place where the annoying people don't go very often. In lessons, though, it's really just a matter of trying to get on with the work. For dealing with bullies, a lot of people say to just ignore them, but that never actually works in practice. It's just school, though, and the important things about school are the people you make friends with and the things you learn. Any effort towards preventing bullying ends negatively (I think).
Even if there's just one sentence there that helps, I'll be happy. My school experience was terrible, and I'm glad to be out of it with most things I consider important intact.