How can I get over a girl that I love so much?

There's this girl. And I love her more than anything in the world, but to her, we are just the best of friends. We tell each other everything, she gets boyfriends, I get girlfriends, but I only want to be with her. Now school is out, and she has moved. Her phone was cancelled, and we can't talk any more. I keep telling myself that I just need to get over her, but I just can't. I get really depressed when I can't hear her voice for a while, and I'm on the verge of losing it. I can't talk to anyone about this because no one even cares about me. Now I NEED to get over her so I can get back on track from this depression. Can anyone help?