The only one that can break you and your girlfriend up is the two of you and if you love each other then communicate about what is happening re the actions of your girlfriend's friend trying to break you up. It is really up to your girlfriend to decide if her girlfriend's bad actions towards both of you are worth keeping her as a friend. There are generally only two reasons for a girlfriend to try to break up her friend and her boyfriend and that is #1 she is jealous you are taking time away from her being with her friend or, #2 she may be in love with you.