Friend problems please help!?

a new girl joined my school at the begging of term and a had to buddy her so i spent a lot of time with her and we soon became good friends but durning this time my friendship group and me and grown apart... they started talking behind my back and telling me i had changed but wouldnt say how? i have tried my hardest to go back to them and make things right but they continue to make fun of me :( i dont understand why apperntly i am rude and selfish and everyone seems to hate me even though i try to be as nice as possibe i have tried to change but dont no what else to do! my bestfriend who goes to a diffennt school is beeing very suportive and said i havnt changed one bit but if everyone thinks that it must be me not them... recently my friend i buddied has started taking me for grantage and i dont like it and dosnt want me to go back to my old friends she is very muniputive.. today i asked why she thinks she can use me and she called me a c**t and said i was a selfish rude b***ch and that everyone thinks so! i feel so alone and i dont no what to do! please help! what if it is just me :( sorry for the long story! thanks