How to support someone with bipolar?

My SO was just admitted to a mental health facility for extreme and very sudden depression and very fast mood swings. Came out of nowhere. He had once when he was a kid, and it went dormant for a while. I guess it is most likely bipolar from what people are saying, he thinks that too.

My poor baby is so scared. He can't control anything going on in his mind and is extremely depressed. The things he has said about how he feels break my heart.

I have been diagnosed and medicated for depression since I was 14, so I know how to talk to someone who had an illness like me, but I need help.

Anyone with any experience, what is the best way to love and support him? I don't understand everything he is going through.