Dear Deja Vue~
He is lucky to have you there for him, it is a huge burden. At least you do not think it is your fault -which is a trap my wife fell into at the start. Knowing it is not your fault can give a degree of confidence.
Has he returned as yet?
I'm afraid I have to echo what I've said before, he has to not only accept he has depression, but actively seek help and cooperate with it, not just self-medicate with weed and disappear when he feels the need.
As for you being burned out, people do keep on going and going, eventually they get to the stage where they become ill, they lose hope, energy and motivation. You might think his absence gives you respite, however if you are worrying abut him all the time it is not helping you.
I may have asked before -what can you do for your own enjoyment, something to look forward to each day when you get up? Something that allows the mind to escape from the pressures and worries of every day?
I'm glad you have friends and family, it does make a difference not being alone