It sounds like you have a strong karmic connection to him. I had a next door neighbor, Molly, that l was best friends with until she moved away. We talked a great deal. She said that out of all that talking I said one thing that was the best thing that she ever heard in her whole life.
I told her that in Buddhism, the worst thing that you can ever do is not rape and kill people but to take drugs.
Why? Because if you rape and kill or whatever, you will learn from it from the pain you feel. But when you take drugs (including medications) it stops you from feeling the pain so you do not learn. The purpose of life is to learn (learn to be happy).
There are many factors that can affect depression including what you do not consume. Some have been cured of it with consuming omega-3 oil. That is fat! So fat cured them. Your brain is 60% fat so Daniel Amen M.D. (the brain doctor) says that it is correct when people call you fathead!
Here is a
webpage all about diet and depression with other ways to cure it. Also it sounds like your karma is to take care of this guy. But you have to make yourself the number one priority. That is the best chance of helping him.
Here is a lesson on being a lifeguard. In the Boy Scouts I had a merit badge for this and did a 5 mile swim, but I leaned the following from
Baywatch (TV show). It is a great life lesson. Say you are a lifeguard and rescuing a guy and a wave comes and is about to bash the 2 of you into a pillar.
Do you put yourself between the pillar and him or do you put him (or her) between the pillar and you? You put him between the pillar and you. If he is knocked unconscious, you can still save the 2 of you. If you are knocked unconscious then both of you die! So the saying is "take care of yourself so you can take care of others." The key is in you.