Every single one-itus I've had in middle school-through high school, now that i'm in college, I would NEVER even consider dating now.
To be fair, I was a chump until my senior year of high school though, BUT, even the smoking hot ones that I really liked in high school, are nothing compared to the girls you will meet in college and the "Real" world. Remember that.
Wait until you're 18-19 in college like me, hooking up with 22-24 year old grad girls, that's where the funs at. Heheh.
Seriously, though, your in high school. Nothing matters in high school and you will never see 95% of those kids again in your entire life.
As for how to fight one-itus? Its tough, and I suffer from it too.
Just imagine that she's an absolute bitch when she's sick, a sloppy slutty annoying girl when she's drunk that makes out with every single guy at parties, and she poops massive loads of shit every time she goes to the bathroom. How nasty is that? Lol.
One-itus is 110% mental. So trying to re-frame your emotions about her and realizing you don't need her and she'd be lucky to have you around in her life is the only way to beat it.
But in all seriousness, you can only fight one-itus with a plethora of girls. So go meet girls, get there numbers, and after getting to know 5 different girls you still really like her, then keep fighting for her. Once you meet these other girls, your game should improve on her too.