I'm letting my girlfriend know she's no longer allowed to have her friend over.
Why would you tell your gf that?
I know my girlfriend's friend. Her friend has a serious boyfriend, who beats her up and she is very jealous of me and my girlfriend
It's wrong to tell your gf what to do. You are going to upset her by doing that.
It's my house and it's my choice who to let over.
That's true, but maybe this friend needs help and she's jealous that you don't beat your girlfriend.