Maybe if he is still living with you, you can encourage him to sit down daily and write his feelings on something. Keep this journal (online, offline, pen and paper) and use it to monitor his mood. Tell him if he really wants to go off, he will have to keep to this journal so both of you can have insight on his mood, and so he can look back to it and acknowledge instability if it is there. It can also be good for you because you won't have to try and remember all his symptoms because it will all be on "paper and pencil."

Also, you have to set rules of what is and isn't proper behavior. Believe it or not I am 21 and still get lectures and punished from my parents and boyfriend. They know without structure I fall apart.