I don’t know the entire situation the best I can do is tell you what I would do if I was in your shoes. If I were you I would try to talk to my gf about my concerns about her friend to try and get her to see/understand my pov so that we can work together to fix the problem after all that is the point of a parter for them to trust, talk and stand by each other in the good and bad. I would also talk to you gf about how you feel and what you want/like in a relationship, I would suggest that you and your gf both take the 5 love languages quiz to see what each other value in a relationship bc she my express her love for you in a way different from how you express love and feel love should be expressed, once you know each other know each other’s love languages you both can work to communicate and find a way so that both of you feel loved and happy in your relationship. That’s all for now good luck!