What should a wife do who committed adultery and repented, while her husband suspects her and is suffering; should she tell him the truth to relieve him of his torment?

You must offer sincere repentance for this grave sin and for the false oaths (al-yameen al-ghamus), which immerse the one who takes them in Hellfire and for which there is no expiation according to the correct opinion. You must also conceal this matter and not inform your husband about it. You should strive to make your husband forget this issue by treating him well, showing affection towards him, and demonstrating true chastity to him.