I'm with Daisyface, humour him. Try to get to know her yourself if you can, broaden the paths of communication. You may find out more about her that you like (or don't) and it can only help.
Meanwhile explain to him that if he wants to have the trust and indepndence to get to travel to see her, he needs to build his skills and demonstrate his ability to look after himself and to also be a good house mate. At a certain age, we switched attitudes to our kids, to put them on a flatmate footing. To live outside the home, they need to have the social skills and abilities to live communally. This means learning the rules, following the rules and learning the self-care skills.
Here are the rules, and EVERYONE under the same roof must follow them:
1) Tell all other flatmates where you are going and when you will be back. Stick to it. This is common courtesy.
2) Work as a team - if A announces she is going to the store and B needs something, B can ask A. THis wouldn't be possible if A didn't tell people. But it goes both ways - if B is going to the store, he should also ask, "Does anybody want me to pick up anything?"
3) Follow house rules - these need to be established by the group for the group. Rules such as whenever you open a packet of something, put it on the shopping list. Whoever does the shopping - anything not purchased should go right back onto the list. Follow any rosters, but they should apply fairly to all. Last one to bed/out the door locks up the house. That sort of thing.
4) Develop your skills and be useful. Take responsibility for your own washing, your own cleaning, your own meals where possible but in cooperation.
The way this works - if the difficult child complains about the food, for example, then they have to put up or shut up. That means they're not allowed to complain until they can do it just as well if not better. "Ok, you don't like what I cook on the budget I have and the other constraints - then show me how to do a better job."
It also is a good idea anyway, to get difficult child to take a turn at meal preparation. This involves choosing a meal (they often love the choice) but it has to be something others will eat, it has to be within the budget, they have to shop for it, prepare it, cook it and serve it. This may need some supervision, but the chef is the difficult child not the parent. It also give the difficult child a good demonstration of why you need to know who will be home for dinner and what time (part of all housemates letting everyone else know their movements).
A lot of the rebellion you get at this age is from the kid insisting they're an adult now, don't treat me like a kid. Often thiscomplaint is with some basis. But as soon as you begin to trest them like an adult in THIS way, two things can happen:
1) They realise they're more of akid than they realised; or
2) they can surprise you and rise to the challenge better than you thought possible.
It's always worth a try. It's also much easier than trying to clamp down and restrict them further.
Marg