Many people here are trying to put down your feelings and make you feel childish, which is not cool. Chances are that since you are young this will probably be an insignificant part of your life, but it doesn't make it any less painful.

If you really think you can't do anything about it then mourn it as long as you need and move on, since you will most likely meet someone later the will fulfill your expectations even more than her. However, I think that there is a lot that you could do to keep the relationship going, even if it's doomed to stay as a friendship.