You are both very young, and in some respects immature. However, her "sleeping around" may well be just a "growing up" phase she is going through (and there's nothing wrong with that in today's social climate) which will one day lose its appeal. She then MAY turn to you for a more meaningful relationship, or there again she may not. But she's far too young to lock into a permanent relationship at present, as are you, so don't waste your youth in fruitless yearning. You should really stop being so obsessed with her and try to broaden your horizons by taking the advice in Sharingan's first response. Good luck, whatever course you take, and I hope your life takes a turn for the better in the future.