Cee, does he have a feeding tube? If not now might be a good time to have one placed so he can get the nutrition he needs. His moods could be due to the malnutrition as well as the inablity to communicate. I would suggest that you talk to the occupational therapist at your treating facility about obtaining a voice synthizer, like a talking computer, it would help give him a voice. My husband had the same problems with the food, but he could not swallow and lost over 35 pounds even with the feeding tube. He was moody at times but was very dependent on touching, which was difficult during the chemo cycles when close touching wasn't allowed for safety reasons. You mentioned Zoloft but I would suggest that his seratonin and cortisol levels be check to determine if his has a chemical depression or an adjustment disorder. The one is treated with medications but the other requires counseling, individual and or family. Believe me things will get better, but whatever happens don't put the blame on yourself, blame is a waste of energy that you need for other things and for yourself.
You and yours are in our prayers.
MaryAnn