Is it really wrong to tell my girlfriend to stop hanging out with one of her friends?
Why would you tell your gf that she has to stop seeing her friend?
I'm jealous of them and it makes me feel like she's out of my league
I understand that you feel as though you have to compete with her friends, but imposing your will and telling you gf who she can and can't see is a bad solution to the issue. Deal with your feelings of inferiority instead.
Okay, I got it, thanks for the advice.
I'm really glad I could help you in making such a great choice. Trusting her to choose her own friends will strengthen your relationship in the long run.