I just recently went through the same thing with my ex best friend when she told me that our friendship wasn't worth it anymore. Sometimes it's just a sign that she was part of your life because you needed her, you needed that rock, but aren't compatible for a life-long friendship. It's going to hurt for a long time, but the best thing you can do is have fun without dwelling on the fact that she's not by your side anymore. If you ever need someone to talk to, I'm here.