This is only a short comment due to time (sorry) my understanding is that he did keep the frustration to himself. He cam back and took care of things, it was only when pressed in MC that he let you know his frustration. This was the honest answer to how he felt. Am I reading this the right way? If so then I think it a good starting point to work on that he expressed it. I wouldn't ask how he feels about things if I don't want to know the answer.

Having been a carer for someone with mental illness as well as physical disability, I think it's ok to be angry, annoyed, frustrated at the illness but not the person. Very hard to separate the two though sometimes.