I started using post-it notes.....I'd write down the name of whoever owned the item, and stick it on the item....after a couple of days of seeing their names all over the house, stuck on random things that had been left out, they all got the hint.....it's not perfect now, but there are significantly fewer coloured squares around my home!!
Don't clean up after him till he notices how messy the house is, and then if he asks why it's his problem
Never gonna change sorry. Minimalist house, ie ***** stuff down to the basics, and separate bathrooms, his you never enter.
don't give him treats until he cleans up
Sounds like it's time the two of you take a break, spend some more time away from one another, give yourselves time to miss each other.
Stand him in the yard and hose him down!