Meesh:
My husband (nasopharyngeal stage four) was much the same following treatment, but I'm not as nice as you. I rode him a lot. Fortunately, he is used to my overbearing personality and took it well. I was never unkind, but I did push a lot and often thru and post treatment. By week three post treatment he began to turn around and was eating by mouth mostly. It seemed to happen overnight.
Then, they hit him with adjuvant treatment number one and boom, same crap all over again. Poor guy was devastated, as well he should be! He is today on week three post adjuvant number two and has turned a positive corner again.
So, hang in there and push a bit but don't shove. :) His ENT told me in the very beginning to encourage the use of anti-depressants and anti-anxiety drugs. We were never opposed to this as I believe it is well warranted during H&N cancer treatments. He never used them, but didn't get to that point.
Bottom line - we are all different and have different experiences. Keep track of his mental state now more than ever.