The main duty of a woman in marriage, the only thing that she cannot deny her husband unless under specific circumstances.
From the office of Ayatullah Seestani: it is the woman’s duty when it comes to her conjugal life and yielding to her husband’s needs (even preparing themselves for sex is part of yielding) to give in to her husband’s lustful needs. There are many ahadith regarding this issue. In the case of her not yielding, she becomes nashizah (transgressor, rebellious) and the rulings of nushuz will apply to her.
The duty of carrying out the marital relationship lies mainly with the women and is of extreme importance; there are many traditions that relate to this matter, here below only a few ones as example.
Imam Sadiq (a) has said: “A woman came to the Holy Prophet (s) and asked him what the duty of the wife is towards the husband? He replied: “That she answers his (sexual) needs, even if they are in the situation of riding on top of a camel.”
Imam Baqir (a) narrated from the Holy Prophet (s) where he told women that: “Do not make your prayers lengthy in order to prevent your husband’s from having sexual relations with you.” In another tradition Imam Sadiq (a) has explained in relation to this aspect of women’s actions and its end consequences that: “A woman who keeps her husband waiting on their place of sleep and does not become willing to have sexual relations with him until he falls asleep, till the time that the man remains asleep the angels will curse that woman.”
(Al-Kafi, chapter “The woman’s rights regarding her husband” vol. 5, pp. 507-508.)
If a woman denies herself physically to her husband for many years, he has undoubtedly the right to ask a divorce and/or to marry another woman.