I've never had to deal with as bad of a problem as you describe. But, as I like things relatively neat and tidy, I tend to clean up and do what I have to do to make me happy and feel comfortable in my living space. If there is something that does not directly affect you, some chore, some area of the house, etc. I would leave that alone until the slob takes care of it - and let him know you have no intention of helping with that, no matter how bad it gets. Like not washing his clothes. If you can do that. This is a tough problem, good luck! I hope someone here has some better ideas for you.