We are glad that you are reaching out for help. You should NOT be treated this way by anyone, especially a friend of yours. It sounds like you have given her plenty of chances to realize her wrong doings, and yet she refuses to stop or make amends. You have gone over and beyond what a friend should have to do, because really you do not deserve this.
The best thing to do at this point is to just be honest with this friend, and let her know that you can not take it anymore. Let her know that you want to stay friends, but she is going to have to make a strong effort to change.
If she is unwilling to do so, then let her know that for now it is going to be best if you two take a break from the friendship. This will give her a reality check, and see that you can not treat people this way and expect them to stick around. Not only will she get a reality check, but this gives you time to spend time with some friends that do not cause you to go home in tears.
Know that you will get through this, with or without her as a friend. If she wants to be your friend, then she is going to get her act together. If she does not want to be friends, then you just need to focus on you and what will make you happy.
You did all you could to make the friendship work, and things have just gotten to bad to handle anymore. Find some friends that you enjoy, and make some plans with them and just enjoy being a youth! If you need anything else, reach out to us anytime.