Alzheimer's patient- how do I keep my feelings under control?

My husband is 91 and has Alzheimer's. I know nothing about this disease and the progression. He certainly is not the man I have been married to for 43 years. He was very very active and creative. Now he just sits and watches tv. He laughs a lot, even when it is not funny. There are times when I am struggling to do something and he will sit there and watch me. Then when I am almost done, he will say, can I help you? He is ambulatory but only gets up to go to the bathroom. I am 77 and have emphysema, neuropathy, and many more issues. It is hard for me to keep up the house, laundry, cooking, etc. So I get angry at him for not trying harder to help. Actually, physically I am in worse shape than he is, so that is why I get angry and will lash out at him now and then. How do I keep that under control?