hey xx
im 15, female and I read your letter, I just thought that maybe you should confront your mum and tell her how you feel and confront your mate aswell, mums never try to push there children away intentionally, she probably doesnt realize it she's probab;y trying to make her feel at home as she is not really your blood. Atleast if you tell your mate and your mum they will be more aware and ypu should see a difference.
love rajnesh