Is it permissible for a man to return to his first fiancée, whom he divorced before marrying her, to atone for his sin against her, after the annulment of his second engagement?

A Muslim must fear Allah regarding the daughters and women of Muslims. The suitor is a stranger to the fiancée, and the engagement is merely a promise of marriage. Nothing becomes permissible for him from her before the marriage contract. The suitor's utterance of divorce does not take effect because it did not occur in its proper place, for there is no divorce before marriage. He can return to her if he deems it good. The way to expiate the sin is through seeking forgiveness (istighfar), repentance (tawbah), and regret, not merely by returning to her.