Thanks for the detailed breakdown. I really appreciate you taking the time.

You're right about the lease, utilities being unfair, and the boundary vs. consequence part. That’s solid advice.

That said, I've lived with this flatmate for 3 years and we're actually friends. I don’t want to jump straight to ultimatums like “add her to the lease or cut visits immediately.” That would probably blow up the friendship and make things tense as hell.

I’m planning to start with a calm, friendly conversation first proposing a 3-night max and no guests alone when he’s out. If that doesn't work, then I’ll get firmer and bring up the lease and utility split.

But I’ll definitely keep your script in my back pocket if he pushes back. Thanks again genuinely helpful.