Here’s a thought:
Call him for help.
When you visit him, put aside the illness as if it didn’t exist for a moment, and ask him for some advice. Think of his region of expertise and talent and tell him you need his assistance.
He is an actor and you are a drama teacher. Ask him how he would approach a difficult scene or how to present a particular character. This will be more than just telling him “you matter and you are needed”, it will be actually making him needed.
Now obviously we are involved here with some serious health issues. They will not go away with a few minutes of conversation. It might not work at all. He may not even be receptive to being asked, or perhaps he is incapable of responding. But if you have even a slight chance of getting through to him, it is well worth the effort. It might give him a short while where he is not being absorbed in his own issues. If he can put his thoughts on someone else for even a short time, that may serve as a little gasp of air, and he may be lifted, if even momentarily, above his darkness.
There are times when the trap of depression or illness is the self-absorption it brings. The best antidote for that is serving others. Help him with a chance to do that. If nothing else, you will have expressed to him that whatever he is going through, he can still contribute to the world, and he is valued enough to be asked. That may be just what he needs to hear.
May he/she get well soon!
Rabbi Mendel Bluming, Maryland and Rabbi Moss, Australia