How do I deal with a pot smoker who won't stay outside with it like he agreed to?

Your house, your rules. Is kicking him out an option? "He says he should be able to smoke where he wants to? Why? Because he's ill. WRONG! Just because you have an illness doesn't give you a blank check to walk all over someone. He needs serious attitude adjustment. Call the cops if its not medical-use marijuana. Have him hauled off.