You may not be able to do anything if he suffers from bi polar or depression he will have to seek guidance of his medical professional and possibly get on some medication, things may not change for the better until he can admit he has a problem and then seek the help. You can suggest that he do that and see if he listens to you. As far as your relationship goes, you are the one who can tell when he doesn't seem ok or just not quite like himself maybe not quite into a bipolar episode, but something just seems a little off, you should be able to recognize the signs of when he is going to be in a mood and what triggers the mood. You've told me some of the signs so now you know when they happen and what he does that shows you that he is in a mood. All you can do is continue to reassure him about the way you feel about him and show him that no matter what you will always be there. You're going to have to check your emotions, it's ok to care, but not overly so; and not when it rolls over into the worry category--because worry too quickly becomes stress, and you don't need that. And he will react to your reactions to them. If you don't worry, neither will he. If your stress level remains low, so will his, don't let him see any negative emotions from you this will make him more stable. Stay positive even when you want to be negative because he needs you to tell him everything will be okay and you don't want to end up depressed also. Two depressed people does not help it makes things worse so try to talk him into either talking to his physician or a counselor so that he can be properly diagnosed and possibly get on medication.