What does a husband want from his wife, when he believes their marriage is destined, and what is the ruling on her remaining with him in this situation?

You must repent to Allah Almighty for the relationship with this man, for such relationships are forbidden, and he has married someone other than the questioner. As for his statement, "This is my destiny," it is correct if he means that what Allah Almighty has decreed will come to pass, for a person exerts effort and utilizes lawful means, and then Allah does what He wills. It has been stated in the Holy Quran and the Prophetic Hadiths that everything that befalls a person is written and predestined before their creation, and that there is good in what Allah has chosen. Therefore, a Muslim must submit to Allah's decree and destiny.