Rowstock78 It's absolutely understandable and sensible that a 29 year old doesn't want to give up their own independent accommodation in order to properly move in with a student they've been seeing only 7 months, and that student's mother.
It is not 9k that he's at yours 7 nights per week using your hot water and electricity - are you also paying for his food? Does he do laundry at yours?
The argument that your daughter "likes her own bed" and therefore won't stay at his isn't a reason for him to be at yours 7 nights per week, and is frankly completely ridiculous.
Do you actually just see this man as a cash cow to subsidise your adult children's living costs?
If it's not that but the understandable unwillingness to subsidise a working adult in a new relationship with your daughter the answer isn't to demand he move in and give you £1000 per month when he doesn't want to make that commitment!
The answer is to set boundaries - no matter how attached your daughter is to her bed, her boyfriend only stays over two nights per week. Your daughter can sleep alone in her own bed or go to his the other nights. If she actually starts going to his(balancing out the use of utilities) you could offer 3 nights - if she's at his 3 nights too that will balance things in both places.
If she likes her own bed so much she has to sleep in it every night she'll have to sleep alone sometimes, until their relationship is long term and stable and they both want to move in together - because they're ready, not because you could do with an extra £12,000 per year!
Btw if he's going to share with your DD you won't be able to reasonably ask for anything like as much rent as he pays to have a room to himself in his flat share!