All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The Muslim woman is obligated to wear the hijab that covers all of her body, except the face and the two hands, when she wants to go out or when she is in the presence of non-Mahram men. Neither the husband nor anybody has the right to prevent her from covering her body that way, in which case the wife does not have to obey her husband. This is evidenced by the Hadeeth of the Prophet reading, “No obedience for evil deeds, obedience is required only in what is good.” [Agreed Upon (Al-Bukhari and Muslim); the wording is that of Imam Muslim]
The husband should deal kindly with his wife. He should not insult or treat her like a servant. The wife has the right to kind treatment, as Allah the Exalted says in the Quran (what means): {… And live with them in kindness. For if you dislike them, perhaps you dislike a thing, and Allah makes therein much good.} [Quran, 4:19] Commenting on this verse, Al-Qurtubi said, “As for the Saying of Allah the Almighty, 'And live with them in kindness', it means to live with them according to the kindness with which Allah, the Almighty, commanded men to observe. This includes fulfilling her due rights, including the dowry and the expenditure, not frowning at her without a valid reason, and kindly speaking to her. The husband furthermore should not harshly speak with her or show that he is inclined to another woman.”
Ibn Katheer commented on the same verse, saying, “As for the Saying of Allah the Almighty, 'And live with them in kindness', it means to kindly speak with wives and deal with them well according to the best of your abilities. In other words, treat her the way you like her to treat you. This is supported by the Saying of Allah, the Exalted, {And due to the wives is similar to what is expected of them, according to what is reasonable.} [Quran, 2:228] The Prophet also said, “The best of you is he who is best to his family, and I am the best among you to my family.” It is narrated that the Prophet used to kindly treat his wives, continually smile at them, be gentle with them and meet all their needs.”
Even if the husband no longer has any desire for his wife due to her old age or any other reason, this does not justify insulting her or preventing her from her due rights. However, he is allowed to get married to a second woman since Allah, the Exalted, allows men to marry more than one woman as long as it would bring about a public interest for the Ummah and a private interest for the couple. If the husband marries a second woman, the first wife should accept his action since it is the law of the All-Wise, the All-Acquainted.
Allah knows best.