How should a man act who has doubts about his wife, who swore by the Quran and her children that she did not betray him, after he discovered that a strange number on her phone belonged to a man living on the same street?

The husband must think well of his wife, and it is not permissible for him to think ill of her without evidence, for Allah Almighty says: “O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin.” This emphasis is further strengthened in the marital relationship. If the wife repents and it is most probable that she is truthful, then he must hold on to her, treat her kindly, and work to protect her from causes of temptation. This is part of the husband's duty of guardianship.

The husband must strive to foster a faith-based upbringing in the home, and work to satisfy his wife's emotional needs and treat her well so that she does not look to others. He may adorn himself for her just as she likes for him to adorn himself for her. Oath-taking is an act of worship, so it is not permissible to swear by other than Allah.