Screw it. Move on and deal. I'm guessing you're like 14? When I was your age (wow can't believe I just said that...) I got my first real sporty bike (500R) and spent weeks and weeks working on it. I would ride every day and it made me feel alive and I loved it. I didn't really start dating hardcore until college which is where I've been with my girl of almost 3 years now.
The point I'm trying to make is that, you're young dude. Shit's gonna happen and you're not gonna get a girl that's really serious until later. If you want a serious relationship go ahead and try. But you're young. Your heart is gonna get raped and you will feel bad. Shit is gonna happen you just have to learn to live with it if a relationship is that important to you. That's the reason I rode so much and worked on my bike all the time. It kept me focused on getting to college and I didn't have to deal with the drama and bullshit.
Do what you want, but this girl isn't into you and it's better if you just let it go and move on. It's gonna take time. Months, maybe years (I dated one girl in High School that took me 2 years to get over. I think I dated maybe 3 girls in HS.) But don't pine away. That's just dumb. Find a hobby that keeps your mind occupied so you don't think about her. Seriously. Girls at your age are gonna be just plain stupid.
Sorry if that sounds harsh, but that's life dude. Shit happens.