I don't really like my "best friend"??

wow, you sound like you enjoy your time AWAY from her much more than you enjoy your time with her and you and her need to realize that that is NOT friendship. Just tell her that when she is mature enough to be a good and supportive friend, you'll be ready to give her another chance. If it's too hard to confront her about it, avoid her. Join clubs that she's not in and try sitting with other people, as for her getting mad about you having plans, that's just plain selfish and childish. You deserve better