I am sorry this happened too. But you have to remember something could of happened in her life, that she just doesn't want to talk about, or has to deal with by herself, or the distance of the friendship is too much for her and she just can't make the trips you talked of.
In the long run, I think you are better off. As they say some people come into your life for a reason, season or a lifetime.
I would just let it go, don't try to analyze it or figure out why, it will only make you more upset, and your mind will wander off thinking all sorts of reasons, when really you will never know.
Nikko