While I agree with your stance, nothing is going to stop him from having overnight guests, but him.

You've said your piece, probably the best choice now is to do nothing.

What is your course of action if you find that he's had someone there overnight?

Me 57/H 58
M36 S 2.5yrs R 12/13

Let me give up the need to know why things happen as they do.
I will never know and constant wondering is constant suffering.
Caroline Myss