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.
First of all, it is an obligation on this woman to repent to Allaah from this illicit relationship between her and that man as this is a grave major sin especially that she is already married. By committing this sin, she both betrayed Allaah The Almighty and her husband, so she must immediately repent from her disobedience and sin and not care about that dissolute man with whom she had illicit sexual relationship. For more benefit on the conditions of repentance, please refer to Fataawa 86527 and 87903.
Also, she is obligated to go back to her marital home, and if she is harmed by staying with her husband or that she hates him and fears that this would lead her to be neglectful of his rights, then it is permissible for her to ask him for divorce or Khul’ in return for compensation; for more benefit, please refer to Fatwa 89039.
Finally, the following two matters should be noted:
1- It is forbidden for a man to spoil the marital relationship of a woman with her husband, and to urge her to ask for divorce whether this is by words or action. Indeed, some scholars are so strict on this issue that they are of the view that it is forbidden for a man to marry a woman whom he spoilt the marital relationship between her and her husband; for more benefit, please refer to Fatwa 92056.
2- Both spouses should be keen on being affectionate and loving towards each other, and them should respect each other’s position and fulfill each other’s rights.
For more benefit on the rights of the spouses towards each other, please refer to Fataawa 85308 and 88304.
Allaah Knows best.