Did the ex-wife betray her husband? And how can the husband ascertain that? And will Allah forgive her if she had betrayed him?

Watching pornographic films and ordering one's wife to watch them is a manifest evil and a clear sin. The fundamental principle for a Muslim is blamelessness, and it is not permissible to accuse them based on assumptions. Allah Almighty says: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin." And the Prophet, peace and blessings be upon him, said: "Beware of suspicion, for suspicion is the falsest of speech." Accusing one's wife of infidelity without proof is serious and carries a severe warning. Allah Almighty says: "And those who harm believing men and believing women for [something] other than what they have earned have certainly borne slander and manifest sin." This could lead to an accusation of slander (Qadhf). The husband contracting gonorrhea or the wife asking for forgiveness does not indicate infidelity. It is advised to cut off these obsessions and not to seek out the wife's infidelity. If he takes her back into his marriage, he should deal with her based on her apparent state and advise her regarding prayer. If she repents and maintains her prayers, then keeping her is better; otherwise, divorcing her is better if she neglects her obligatory duties towards Allah or is not chaste.