I'm at the tipping point and don't know what to do please can I have some advice asap

Right girls I need some help my ex best friend has been going through a really hard time (her sister committed suicide on March 17th 2017) I have been there for her through every thing and I have torn my life apart to make her even the smallest bit happy and she is a very over powering confident girl and I hate the face I lost her but because we are both strong characters we disagrees on something and she has made a massive deal out of it and now I am left alone all break and lunch and am starting to feel really depressed again because she is treating me like shit and taking all my friends away from me so I want to move school but I can't because this is my forth school and I have already started my GCSEs and really don't know what to do (I am feeling sick because I don't want to be in a room with her so I am not going to my classes anymore) and I just need help on what to do.

(I'm 14 and I have really really bad dyslexia so I'm sorry if it is hard to understand)