Is the husband considered an oppressor or oppressed in his treatment of his wife after discovering her repeated infidelity and his refusal to divorce her, and is the second wife's request for divorce considered unjust if the husband returns to his first wife?

It is permissible for a husband and wife to agree to maintain the marital bond without the husband giving all or some of the rights [due to the wife], but this option is not advisable for a husband who has a young wife who has previously engaged in illicit relationships, as it may lead her to corruption. It is more appropriate for the husband to guide his wife and help her maintain chastity. If she becomes righteous, then that is good and excellent; otherwise, he should divorce her.

As for the second wife, it is not permissible for her to seek divorce merely because her husband has returned to his first wife, unless there is a valid excuse. However, it is not an injustice on her part to reject a polygamous husband. Nor is it permissible for her to demand the divorce of the first wife.