So he is depressed because you are depressed and not working and have back problems!!! So is he trying to say his depression is all your fault? And you have to just stop being depressed and take care of him? His Doctor doesn't think he needs meds, so the doctor must not think he is all that badly depressed. Yeah, I am sure it is stressful for him. We depressives are not easy to live with.
But sorry Gabs, you have a right to be selfish. You were drowning and have just barely managed to grab onto a flotation device. He will drown you if you try to help him at your expense. If he is depressed, he needs to seek help and if jointly seeking help works, that is great. But you are not ready to be his support system. You can't throw that life preserver until you are on solid ground yourself.
He needs to seek help and help himself, like all of us here are trying to do.
Harsh? Perhaps. But you need to protect yourself first.