I echo what they said above. I've learned that when someone in my life says 'its over', they mean it. I shouldn't try to convince them otherwise. Her sexual identity may have something to do with it. At her age, it is a good possibility that she's confused/exploring. ( I know I was). And the LGBT population unfortunately has a higher percentage of substance abuse. But its not an excuse, and regardless of why she is acting this way (i.e. blowing you off, drink ing way too much, etc.) its good to stay away from her. Time will tell.
Thanks for sharing your story!