Please put yourself first and do not bow to his pressure to allow him to move in with you. It will not end well.
At least at the moment you have independence, space from him and boundaries. If he moves in with you then you’d lose all that and he might start using in your property.
I really resent the fact mine does it in the property – I don’t want to be around it and even if you are never in the same room when they are doing it, I believe it still has a residual impact as it gets in the air and on surfaces and the floor etc.
Plus when they use like this, they become dysfunctional and you have this person either on it in your property or on a come down in your property. It’s horrendous.
Do you have any nice times with him? Does the relationship still feel worth staying in?