Apparently someone I considered a best friend told me she thought it would be best if we were not friends anymore

The thing that sucks is I did EVERYTHING for this friend. Granted, she told me she appreciated it all, including buying her book for her class so that she would not fail, sending her money, and items here and there (she is a nursing student), and I did everything I knew how to do to be a friend. When she would go out and get herself distracted, I would harp her that she should be studying instead, and then I get this.
I'm sure a lot of you will say she was not much of a friend, but she was a pretty good friend to me for a while. She did help me out on a lot of things, but I guess the thing that confuses me, is why she did this.
Either way, I'm announcing it to the world that does not care, and you all can feel free to post Cargo Bays, and Give-a-damns.
I guess what I may need to know is why I am not sad about this? Shouldn't I be depressed, or a little upset over this? Is there something missing? Are my feelings burned out?