Is it permissible for a husband to disclose his wife's secret which she asked him to conceal, justifying that by saying he knows best what should and should not be said?

A husband's disclosure of a secret is impermissible and sinful, because a secret is a trust and disclosing it is a betrayal. The Messenger of Allah (peace and blessings be upon him) said: "If a man narrates a hadith and then looks around, it is a trust." (Narrated by Al-Albani, who graded it hasan). It is forbidden to disclose a harmful secret. The husband must repent and seek forgiveness for what he has done. It is advisable to show him this fatwa and not allow this matter to disturb the serenity of the marital relationship.