Ref. No. 1005/41-175
In the name of Allah the most Gracious the most merciful
The answer to your question is as follows:
The woman must always obey her husband as much as possible, and try never to avoid when he calls for bed. If a woman is really sick then you should arrange a better treatment for her. How can you obligate her beyond her capacity if she is not in good health? You should try your level best to maintain your married life with good conduct. If you are still not able to overcome on your desire you can keep fast to control your passion. Divorce is not a solution for the problems.
ولو تضررت من کثرۃ جماعہ لم تجز الزیادۃ علی قدر طاقتھا۔ (الدرالمختار مع رد المحتار 3/203)
And Allah knows best
Darul Uloom Waqf Deoband