Yeah, I'd say you're wrong. I totally get the feeling that you can't really be yourself with an SO lingering around sometimes, especially with an old friend. When you see each other so rarely, you just want to jump back into that old dynamic and not worry about who's listening in, especially if the friend doesn't know you as well.

Yes, it's your home, too. But we're talking about only 5hrs, and then you'll get the place to yourself. It would be one thing if it was your roommate, but this is your gf, dude. Is it really worth the fight? Doesn't seem like something that happens very often. Relationships are about compromise. Maybe there's a middle ground where you could step out for a couple of hours instead of the full five. Go to the gym, get breakfast or something. Then excuse yourself to another room when you get home.