I suggest telling him that when he has his own place, he can look at porn all he wants, but until then, he needs to respect your home and your rules. Also, he could look at it at a consenting friend's house, if it's that important to him. If he has an addiction, then he needs to get help (and no, just because he likes and demands to look at porn doesn't make him addicted). If he refuses to follow your rules, I'd tell him to find his own place then. I know it's tough, especially if he doesn't have the money to do so, but you have to make choices in life, and he needs to learn that.