Why do girlfriend's friend(girls) dislike me?

I mean when I talk to my girlfriend and stuff. Her friend be like they don't want talk to me. Then 2 month later you are like hey I wanna hit up with you and her friend and her just don't talk to to me and don't know why to my girlfriend too. I mean I alway talk to her everyday. And her friend say she don't wanna talk to you and she don't like you. Like WTF and my girlfriend spend more time with her than me . like what her problem and my girlfriend she don't be wanna reply back to me sometime on Facebook. Like two question what her (friend) problem and what should I do to my girlfriend now. I getting tired of this bullshxt. Please help me