It does sound like depression. It isn't you and it isn't that he doesn't want to be your friend. This lack of interest in, well, everything including hanging out does not mean that he will remain this way or that he is ditching you. With bipolar we take meds and see psychiatrist or therapist to better help us control our moods and hopefully not slip into these extremes, but it does happen. Your friend should get in to see his doctor. This situation you are in requires patience and understanding. Good luck.