Aww, sweety. I don't think you should count on her waiting around for you. She's a young girl who needs a lot of attention, which to be honest, is normal for a girl that age.
I think you should enjoy the time you have left until you leave, and then break off with her. You can get back together again when you return, if you are still interested, and who knows? you may even meet someone else while you are away.
I'm sorry.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?