Welcome to the forum, Lucinda. Wolf is correct, grays are usually one-person birds but you can still have a flock mate relationship with them as long as their chosen one is not around. I have a Timneh grey that chose my husband over me years ago and, although she doesn't bite me, she would if I tried to interact with her when she is with him (and he doesn't even like birds! He is actually terrified of them).
I suggest that you don't take this personally, accept the situation as it is and be happy for her because she did find somebody to love even if it's not you. Mind you, even though this is my recommendation, I am very aware that this is not what you wanted when you got her, that your feelings are hurt and that it's a very bitter pill to swallow! I've kept parrots for over 20 years, love them to pieces and understand them a little bit better than most people so I know, on a rational level, that it's nothing personal against me but I still tell her all the time (and in a sulking tone of voice, too) that she chose the wrong human -as if she understood or even cared
