One of the closest people to you has depression and bipolar. These things, if left untreated can/is having a devastating affect on both them and the people around them. However, they refuse to acknowledge that there is anything wrong with them, and don't do anything about it. What would you do?
Strongly encourage him to seek help. If necessary, I might offer an ultimatum
"If you don't seek help, I can no longer spend time with you or take your calls."
"If you don't seek help, I can no longer spend time with you or take your calls."