Does he see a therapist?
When I kept having deep depression while on Prozac (and yes, dosage changes were done), I decided to stop taking it.
In my mind it was "Take a pill and be depressed" or "Don't take a pill and be depressed."
So I quit and now I am just in therapy.

I would just gently repeat during calm times that you wish he would consider taking medication again, because you want him to feel better. Ask if he might be willing to just try it for a while again, to see if he feels better. Then after that, he can decide where to go from there.