What is the ruling on a wife maintaining a relationship with someone from before marriage, while having a child, knowing that the husband covered her after discovering she was not a virgin?

A wife establishing a relationship with a foreign man is a great evil, an act of disobedience to Allah, and a betrayal of the husband. If this is proven, the husband must confront her, admonish her, call her to repentance, and sever the relationship. If she repents, then praise be to Allah. Otherwise, it is preferable to divorce her. A virgin is one whose hymen has not been ruptured in the vagina, and this has no relation to the anus.