I don't know what to say to help. I'm still kind of thinking you should go ahead and get him into a nursing home. You can still go and care for him there. That way you have a chance, on your own, in your own apartment, to build on your life. Get out to groups if there is those. I know its easier said than done. I know how much you want this one thing to end well for him.
I know depression sucks the desire out of you already, as it is, to do things. If you were on your own and part of the problem is loneliness and the need to have a job to do, can you try other ways to build up your self worth, like a hobby. Maybe pick up a musical instrument. Maybe gardening a little. But i think you especially need some close friends. Where can you start with that? Join a caregivers group and possibly use the time when the support worker is there to go out to a group like that? You need support, and forums are not enough for that. If it wasn't for me continuing to call my long time gfs, I would have no one to vent to except my bf, who is very very tired of hearing me talk about my life.
You could also try, med-wise, the suggestions here and slightly tell the psychiatrist that you believe those meds will improve your life. Be sure to really relate that things are not "OKAY", and tell them how deeply depressed you are so much of the time. I wish you well, I wish there were concrete answers.