I'm not going to allow my gf to attend game night with my guy friends
Why do you not want to spend game night with her too?
I don't want her around all the time. I need time with my guy friends.
It's okay to want your alone time with friends. You should set that boundary with your girlfriend. She should understand.
Having her miss out is a small price to pay. It's her commitment to me, who cares if she misses a game night.
I think that every one needs to have nights out with their friends. I see no reason why it would not be okay to have a guys night.