My (ex) best friend goes behind our backs and tells our personal info and crushes to everyone.?

So i just found out today that my ex best friend went behind my back (after I made her promise not to tell anyone) and told my crush (my best guy friend) that he should ask me out. There was a reason i didnt ask him out, he liked someone else and I respected that so I didnt tell him. But i told her thinking that (after she promised) she wasn't going to tell anyone.. Till my crush messaged me and told me that she went to his crush and told her everything that she wasnt supposed to tell anyone.. She went behind both of our backs in one day about our personal business. We should be able to trust our friend to not tell everyone our secrets.. Now im pissed and I told her that what she did was wrong and she has yet to apologize.. Ive decided to not talk to her ever again.. Which will probably be hard since I have a lot of classes with her but i need advice or if u all have personal experiences can you tell me about them.. I just dont know anymore.