OP I'd recommend talking to him openly about the disorder he has been diagnosed with. If he, or the family, don't know much about the disorder , or the prescribed medications, or their side effects, you have a lot to work on.
Some people with severe mental disorders become extremely expert at its symptoms ( the worst they have to contend with; the ones they don't)'. They know a great deal about their medication , it's upsides and downsides, side effects. They may be painfully aware of what can trigger episodes. They may be the expert on how they want to be treated during an episode; left alone in peace; NOT left alone; total silence; white noise.
Only a few decades ago, cancer was so unmentionable people wouldnt say the word let alone admit they had it. Now we know that open-ness and talking about cancer promotes the best outlook to cope with both the diagnosis, the treatments, and living with them. Now we know cancer treatments can have awful side effects that are very hard to endure.
Not so many people know, that some mental illness treatments also have miserable side effects . nobody likes to mention.
Talk to people with mental health diagnoses. Give them a chance to explain what it feels like from their side, what's going on with their treatment , and what they need ( or don't want) from you.