Dana, it is natural for both of you to be depressed and discouraged. Sleep deprivation is a big factor in this. You have gone through a lot, with the idea in the back of your mind that when the surgery was over the whole episode would be over. NOT
The good news, as you both know, is that he is as close to being cured of this cancer as it is possible for him to be. It will take a while to get normalized.
I don't remember how old your children are, or if they are located near you. Do you have someone...a relative, friend, male friend of your husband, who could come over and "visit" with him while you either take a nap or go out for a cup of coffee or even go to the grocery store, ALONE? You absolutely must take care of yourself or you will be a failure as a caretaker.
As for your husband, it wouldn't hurt to mention to the doctor that he is depressed...and, while not able to diagnose in person, I am sure that he is!! And then, be encouraging, empathetic, but don't encourage the bad feelings. Anything that can cheer him up, without his realizing you are cheering him up, will help. He needs to know, from others on this forum, that it will take months for things to become normal for him. He is already ahead of many others at this stage.
Remember, take care of yourself....even if it is a nap instead of getting the dishes done....and we are here for you.
Sara Anne