Well, at least you all met and everything was out in the open, including the discomfort. I think you can't really do anything to help him deal with this; your GF has to take care of her relationship with him. If he wants to set up rules or boundaries that limit her involvement with you, then it would seem to me that your girlfriend needs to discuss it with you and your wife, and you all need to make some choices about what you can live with, what you and she wants. I'm not experienced in poly, just starting out on this path myself, but I think that even if you bend over backwards to try and make him happy and comfortable, you can't control how it will go -- and it's his stuff to process, really. And she will decide if he's someone she wants to keep in her life. I would just be yourselves -- don't walk on eggshells around him, be as affectionate and caring toward your GF as you want to be, and let her worry about him.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein