MG, this may be common knowledge to everyone but me, but how old are you? If I'm guessing correctly, you're still in high school? Let me reassure you with a simple statement:
Breaking up sucks.
If at any time, you try to make it not suck, try to get your mind off it, or try to demonize your ex, stop. You're going to feel crappy, you're going to be reminded about it by everything, and your ex is the same person she always was (which may or may not be a good thing, but her taking the initiative to break up with you does not necessarily make her a monster).
Cyborg referenced up there the saying "Time heals all wounds", and this is mostly true. Scars never heal, but after a while, you kinda forget about them, until you remember, and then you reminisce a little and go on with life. Last year, on my birthday (2005), I met someone who would eventually become my girlfriend, via distance. Now, you can all say what you will about e-relationships, but as far as they go, we put the effort into it. I'm talking nightly IM chats and phone conversations that went into two or three hours easy, almost every night. Web cams, letters, and eventually, face to face visits. She drove almost 300 miles (one way) to meet me. I was serious about it.
And then came the day after Christmas, when after two inter-state visits and almost a year of correspondence, she gave me that I-love-you-but-I'm-not-in-love-with-you crap. Right as I was jumping through holiday hoops at work to spend new years with her. I was pretty devastated for a while, but the fact that she became really unpleasant afterwards made it easier to disconnect myself from it all. It took me a few months to clear my head and get over it all (Moocow knows about this), and after I finally stopped getting angry text messages, I got a new girlfriend and have been happy ever since.
I don't know your situation, but I'm sure it's different from mine. That limits my ability to help, since the above story is about the only time I've ever been dumped, so I don't have any other tales to tell. But there are a few lessons to be learned, I think.
1. Long-distance relationships can work, if you put forth the effort.
2. Any relationship can fail, even if you put forth the work.
3. You can't control how someone else feels, or the choices they make.
4. When a relationship goes bad, it's hardly ever mutually agreed upon.
5. It may seem like the end of the world, but it won't feel so bad in retrospect.
6. Life happens, both good and bad, when you least expect it.
Maybe in time, you'll be able to be friends with this girl. Maybe not. Don't feel bad if you can't go back to a more platonic relationship. You shouldn't feel guilty for things not working out any more than she should. Remember that the longer you spend grieving over the death of your relationship, the more time you'll lose that you could be spending not being bummed out. Thinking that won't cure the hurt, but it will help you recover faster. Be logical, not emotional. Your relationship is over, and it cannot be resurrected by any amount of tears. A harsh truth, but a truth nevertheless.
You'll find the right person eventually, MG. And when you do, I promise you, you'll wonder why you ever felt sad.