I am not sure if I can fully understand what you must be going through because I am losing a Father not a Husband. All though no matter how the loved one is related to us, we all go through many of the same emotions, it is just a very different kind of loss that we experience.
Husband's are our partners, best friends, and we do spend everyday with them.
I would think that what your husband is feeling is anger. He is tired of being sick and tired of the treatments that aren't making him feel any better. The anger, does cause depression and a feeling of giving up. They just get tired of fighting. In your Husbands case, it sounds as though he may still have a chance to fight this disease and be able to spend more time with the ones he loves. Don't let him give up, he is internalizing all of his feelings, and he has to let them out. Sometimes outside support helps, but not everyone can talk to a stranger.
Most importantly, you have to take care of yourself too. Obviously the way he is acting is taking its toll on you emotionally, and sooner or later physically. When my sister was dying of a rare cancer at 26 years old, she was angry at everything and everyone around her. You could not say anything to her that made her feel better, she was just bitter. Your husband is young, and I am sure he is thinking how unfair this disease is. He is too young to be faced with the possibility of leaving this world and leaving his loved ones behind, especially you. I am certain he doesn't want to give up the fight, but right now, he feels so helpless and tired. We all have to remember that when you are the person with the cancer, they have a strong feeling that they are somehow letting us down too. They are worried about what will happen to us should they lose the battle.
You and your Husband are in my thoughts, and I hope he realizes how much you love him, and is able to get through this stage of anger and depression.
Much Love Coming Your Way,