Dude, it will be okay. Your only 13. You'll get your heart broken and repaird. There is not much you can do. You just have to keep moving on in life. You'll find other girls in life.
It's your first heartbreak and sadly, it most likely won't be the last. You're young and there's plenty more girls out there who would love to be with you. Don't dwell on it. Just forget about her (though I know it's not easy) and get on with your life.
Awh, it sucks, doesn't it? Well, I know it hurts, but you have to get over her. I know, easier said then done, but you can't live the rest of your life thinking about her. Your 13. It'll take time to get over this, but you can't let this time interfere with the rest of your life. This is why it is usually good to stay away from all the boyfriend/girlfriend stuff. /: