OP, some other posters have kindly said it....this really is about your control of the situation and possibly him in general. I do kindly think you are co-dependant too as another poster said. If you did not tell him the rules ahead of time, he couldn't possibly know what they are. Cardinal rule: never assume. You said yourself that if you had met her a few times it might have been better. It is now about you and not him. By being involved in his everyday life like this, the boundaries are terribly blurred. It is very difficult to give him all of the freedoms that you have with your home/vehicle, etc, but then show your disapproval because you haven't met her = control. You can't control these choices and you'll be so much happier if you let him go, even if he struggles. Of course you can have rules and should, but your mistake appears to be that you didn't have a sit down with all members of the family living in the home to understand and agree to the rules. If he can't agree, he can leave and you should encourage him to. If he struggles, he will be stronger for it. Best of luck OP.