hi, i have been really close friends with this girl and i feel this other girl is somewhat taking her away...

The girl who is becoming good friends with her bullied me in year 8 to the point where parents got involved. she has had a history of blocking people out of friendships before also she was really mean ( bitchy to me but not to her) to the friend she trying to become close to. but she became quite good friends with me (but i now feel like she was friends with me to be friends with her!) She seems to have a different personality with everyone who she is with and with her main group of friends she is quite bitchy !! 

Am i over reacting and what can i do to get my best friend back?