OP
You should not have considered moving in with someone you cannot be absolute clear about money with.
You are asking to be taken advantage of.
He should be offering and pushing money on you to pay his share.
If not, you have moved a waster into your home.
Do not put him on the tenancy.
Mind home and independence.
You have a good deal, protect it.
Someone going on about how much they will safe is a bit of a red flag already.
How long are you together?
Is he very very good at paying his share?
If he is even the tiniest bit tight, you have made a mistake.
Be careful.
Protect yourself and your home.
He should be saving YOU money, NOT the other way round.
If YOU are not saving money, then you are being used.
Lots of men use women this way.
Do not be a mug.
The fact you feel cheeky mentioning it, means YOUR boundaries are not great and you are vulnerable.
Search Cocklodger on MN and read the many many tales of women who were used.