Wife is treated badly by husband who has relationship with a married woman
2-2-2012 | IslamWeb
Question:
Assalamu Alleikum, I recently discovered that my husband is having a years long relationship with a married woman, formerly his fiancee thru intenet video call, phone call, and I also discover the reason why for more than 7 years he's never treating me like human, inspite the fact that I am a sole provider of our family. I have caught their messages that they're madly inlove to each other and saved it. Will it be a reason for me to file for divorce and gain custody of my kids? According to the woman who admitted to me, my husband told her that he never love me, and he is sleeping with me just thinking about her all those years. Is our marriage still valid or not anymore?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
This misconduct from your husband – if confirmed – does not affect the validity of the marriage. However, he is absolutely wrong and sinful for establishing a forbidden relationship with a non-Mahram (marriageable) woman, as this is the conduct of the people of the pre-Islamic era of ignorance in taking lovers, and Islam forbids it.
For more benefit, please refer to Fatwa 81356.
You should advise your husband in a gentle manner and remind him of Allaah The Almighty. You should also clarify to him that such a conduct is wrong and that it has unpleasant consequences. Then, if he repents to Allaah, praise be to Allaah, but if he persists on what he is doing, then you have the right to ask for divorce. Indeed, the jurists 
stated that the dissoluteness of the husband is one of the reasons for which the wife is permitted to ask for divorce.
In this regard, please refer to Fatwa 88408.
Finally, the following matters should be mentioned:
1- A husband is Islamically required to have a good marital relationship with his wife. If he mistreats her, he is breaching this Divine commandment. For more benefit, please refer to Fataawa 86618 and 88304.
2- The husband is obliged to spend on his wife even if she is rich. However, if the wife fulfills this obligation [of the husband] out of her own free will, then she will be rewarded. For more benefit, please refer to Fatwa 86646.
3- In case of divorce, the mother has the right to foster the children as long as she does not remarry. For more benefit, please refer to Fatwa 82128.
According to the most preponderant opinion of the scholars it is not permissible for the husband to think of (or imagine) another woman when having intercourse with his wife, as this is a means that could lead him to becoming attached to her and tempted by her, and there are many evil consequences of this.
Allaah Knows best.