My stepson is driving me crazy!!?

He is 21 and a complete slob. I have tried to lay down some basic rules, keeping your own messes clean, no smoking in the house, etc... he just doesnt care. Everything he does aggravates me! My husband does not want to discipline him or even tell him about things that he should not do (leave wet towels on floor, garbage everywhere, forgetting to lock the doors) because he says that he wants to have a good relationshio with him and not always be down on him. I get this, but what can I do to make everything not drive me nuts!! Ive tried talking to him myself, but then he gets mad, and alienates himself from his Dad (i swear its a guilt thing which totally works!) So im at a dead end, how do i let go and dissociate from how i want to react so that im not so stressed out?