One thing I have noticed from your posts OP is that you seem to be avoiding questions like “when does he see his DFriends”, “what about his hobbies” and “does he have a PT job”.
I’m suspecting that he does do any sport or hobby and has dropped his friends?
If so, that is really, really unhealthy. Do you and your DH see friends and have hobbies?
I’d look at taking him out at some point this week, somewhere neutral like a coffee shop. Ask him how he thinks his exams are going, if he’s thought about Uni, and what his plans are for the Summer.
Some of the Uni open days are open now, for instance Lancaster has one on 4th July.
Visiting Unis might make him start to think of life beyond his bedroom.
I’d also question what he’s doing over the Summer. Graduate apprenticeships, internships and Graduate jobs are becoming increasingly scarce. Out of my DC and the young people we know, you either get them through nepotism or by having a good work record. Employers no longer seem interested in people who have never worked. I do appreciate though that finding work over the summer can be difficult. Perhaps he could do a tour of the local pubs and restaurants to see if they need a glass collector or food runner? The local charity shops might need a volunteer one day a week?
And I’d also question him about contraception. If she’s nice and comfy in your home and it’s very low demand, I’d be worried about a baby.