Yeah, I’ve felt this feeling. I fell in love with a guy the summer before grade 10, and I basically loved him until I graduated from High School. I went out with other people, forgot him for awhile, but that never lasted long: I always came back to loving him! He didn’t love me. It made me miserable, too. The only thing to do about it is try to think about other things and let time work its magic.
I disagree with the others that this is a maturity thing, something you’ll grow out of, or just to do with hormones. This can happen to anyone at any age.
Either way, you will get over it, eventually. It’s like when you get an itch in a ‘private area’ when you’re in public: you can’t scratch it, and focusing on it is intolerable, so you just have to force your mind onto other things, and eventually you’ll have forgotten all about it.
My last piece of advice is not to do anything out of desperation, because you’ll only make a fool out of yourself. Consider confiding in a friend – having someone to talk to will make it easier to stave off desperate acts.