I want my gf's gay bestie to stop groping her
What does he do to her?
He touches her boobs or he hugs her from behind.
It is reasonable for you to be angry when another man gropes your girl. You should ask her how she feels about it before you take action.
It makes me sick but it just confuses her.
Even if her friend is gay, it is still assault. You should help your girlfriend out if she feels uncomfortable.