Without knowing context there's no way to tell. Longterm friendships do end when people get hurt, even friendships as close as you describe. Is your anger out of proportion to what actually happened between you and your friend? The fact that you say you can't find one thing good about her does sound like it's coming someplace other than just hurt. That's usually what's so upsetting about fall outs with loved ones and friends - we like so many things about them but can't get past one thing that happened. So your switch from closest friend to hating her does sound a little more like its part of your illness.