Really good advice so far. I'm female, and I agree with Faerluna that she's probably just letting you down gently. Then again, I don't know the nature of your relationship. How good are you guys at communicating? Did you see this coming (i.e. she's been acting weird, sad, etc) or was this out of the blue? If you saw this coming, it might be the end of the road for you two since you haven't been able to fix it. If this really surprised you, then your communication has probably been lacking, and it might be a good thing to wait a bit (to not be too emotional about it), and then try to talk to her and see why she is feeling that way.
It may be that you just aren't for her, or it may be something you two can fix together.
The best thing is to not ruminate and think too much about her and anything that can bring back memories about her. Do some things you haven't been able to do. Thinking about something else allows you to distance yourself, and the feelings you feel will not be as painful.