Will God answer the prayer of a girl with whom he had an illicit relationship, then left her after feeling guilty, because his family refused to let him marry her and because of her bad conduct, despite his repentance and remorse? And will harm befall his family? And how can he atone for his sin and clear his conscience without marrying her?

Forbidden relationships are a gateway to discord and the commission of indecencies, which is why the Shari'ah has emphasized strictness in interactions between non-mahrams. If you raped her, you have wronged her. If she did it willingly, then she has no right over you. You are not obligated to marry her according to Shari'ah, and fulfilling a promise is commendable. If you are able to marry her after her repentance, then do so. It is not necessary for the fornicator to be punished among his family in the same way he acted, especially if he repented with sincere repentance.