Hey Snidely
Sorry you're hurting. Hope I don't overstep but since you say you were thinking of leaving her before, and now you're in pain because SHE said she might want to break up...I think it might not be so much the loss of her that you're hurting over, but the fact that it isn't YOU doing the choosing? (I speak from experience....heh) Just something to think about, sometimes separating ego/attachment from a true desire to actually be with the person can make the situation clearer.
Wishing the best for you