Hi,
I agree with OronD and Tiptopmanager. Your wife needs your love and attention. You had the marriage vows for you to remember. She has given you devotion and love for the last 30 years. Give this back to her now, not cheating or even the thought of cheating and being with another woman to have sex with. I think this society has put a lot of emphasis on sex and selfishness. It seems like the only way to feel happiness is getting sex and having orgasms. This society does not give into consideration being happy with ones spouse is sacrificing ones human needs when one cannot provide sex during illness. I think if I were you, I would be happy just to be with the person you love, being close and available to provide the care that she needs. Life and marriage is not all about sex.
What would you do if the situation is the other way around? You have the chronic illness, you can't provide her sex, and she thinks of cheating you? Do you think you'll feel good about it?
Be considerate and be a thoughtful husband.