So no,ds won't be going off for weekends with his girlfriend.
But I've been trying to point out, calmly and politely, that parents don't have that level of control.
I wanted to do exactly this at that age - I was 17, GF was 16. DF put his foot down and came with us! It was mortifying. Separate rooms, of course, at the insistence of our chaperone, when we weren't even planning to have sex - we just wanted to share a bed and be alone together.
But that was half a century ago. The age of majority was 21 and parents had the absolute right to dictate their children's behaviour. Such is no longer the case. The following extract is from Wikipedia and I'm annoyed with myself because I once found the original source but don't seem to have bookmarked it. But it's a House of Lords ruling from 1985 - more than 30 years ago. Unless I have misunderstood, or there have been subsequent changes that I haven't discovered, young people have the legal right to make their own decisions as long as they are "competent", and competence is assumed from 16 (hence the right to leave home, obtain an adult passport, etc.). So I'm pretty sure parents cannot legally say no, and the fact that their children still live at home and are dependent is irrelevant, because parents have to support them anyway. That's the whole point of the concept of Parental Responsibility.
Gillick competence ruling in the case Gillick v West Norfolk and Wisbech Area Health Authority, which sought to decide in medical law whether a child is able to consent to his or her own medical treatment, without the need for parental permission or knowledge. A child is defined as 16 years or younger. The ruling, which applies in England and Wales (but not in Scotland), is significant in that it is broader in scope than merely medical consent. It lays down that the authority of parents to make decisions for their minor children is not absolute, but diminishes with the child's evolving maturity; except in situations that are regulated otherwise by statute, the right to make a decision on any particular matter concerning the child shifts from the parent to the child when the child reaches sufficient maturity to be capable of making up his or her own mind on the matter requiring decision.