I'm going to tell my brother his girlfriend is not allowed at our house anymore
When did he bring his girlfriend over and why?
Due to a miscommunication. I thought he brought a friend to study with, not a girlfriend
It's okay to set boundaries about who's in your home. Your brother should have communicated clearly that he would be bringing his girlfriend over so you knew.
It doesn't matter. I know he's going to get back at me somehow.
Your brother shouldn't try to retaliate because you're asserting a boundary. That sounds a little toxic. Maybe you can have a conversation with him about why it's important to you?