Well the thing I need advice with is how to get over someone. Like two years ago, there was this one girl that I absolutely loved. She was like my best friend and we both had romantic feelings for each other. We would literally talk to each other 24/7, spend as much time together as we could and when we could not be together we would be on the phone all of the time or text messaging each other. We knew everything about each other; our deepest fears, embarassing things, ambitions etc. No one knew me better than she did and no one knew her better than I did. But, for some reason I cannot remember, we got into a bad fight, and so, we stopped talking to each other for like a year. But then after that year went by, we finally started talking again and saw each other a couple times. But, now it feels like we are absolute strangers. That special bond we had is entirely gone and destroyed; it is like we've separated into two absolutely different people like strangers that can barely hold a conversation with each other now. Oftentimes I find myself scolding myself for allowing us to have that fight and screwing this all up.
Actually, this IS something I have a lot of experience with and have sound advice for. Unfortunately, all the advice for this sucks. That's just the breaks.
Strong emotional attachments trigger pleasure centers in your brain and release chemicals. The closer you are to having gone through puberty the stronger these chemicals will be. There is one surefire cure for this...time. Sorry bro, but time is the only cure. If I calculate correctly this happened when you were 14. The first girl ever to shoot me down was when I was 15. That hurt horribly for months and I would have the pain resurface YEARS after the fact. But it will go away. 12 years and 30 days have passed since then (yeah, I know it's pathetic that I know that...) and I honestly can tell you I feel nothing. Actually, I probably haven't felt the pain from this particular instance in seven or eight years, but you get my point. This girl of yours will probably never be forgotten, nor will the pain be forgotten, but there will come a point where you WILL NOT feel the pain anymore.
As for future occurrences, you probably have a good number of them ahead of you. Two things make the pain lessen each time. First is age. As you get older the chemicals become weaker. The hormones die down. I still get depressed but it is a bit less painful each time, and none of the recent rejections have felt as bad for as long as that first girl. Second - experience. The more times you get hurt by a girl the more you get deadened to it. You will emotionally invest less and less quickly and rejections will soften in their effect.
So keep your chin up. Life will always suck, but you will get used to it and won't let it affect you!
(BTW, none of this will probably do you any good, but that's how it goes. Plenty of people gave me this info when I was your age and it didn't help a damn bit. But now being older, I am thankful that I received the advice, so now I am paying them back through you, and in eleven years I expect you to do the same!