Will the repentance of a young man who exposed a girl's past out of revenge be accepted after he had loved and advised her, and what must he do to repent?

Firstly: The relationship between a young man and a woman who is a stranger to him is forbidden, and loving a non-mahram (definition) woman corrupts one's religion, mind, and body.

Secondly: The questioner's anger and desire to take revenge on the girl, expose her secret, and strive to spoil her engagement are mistakes and forbidden acts. He has violated her privacy, backbit her, and sought to ruin her affair. The Prophet, peace be upon him, defined backbiting as "your mentioning about your brother what he dislikes," and it is among the major sins.

Thirdly: If his repentance is sincere, then he is obligated to do everything he can to rectify what he has corrupted. The first of these is to seek forgiveness for her and ask Allah to accept her repentance and rectify her situation.

Fourthly: He must strive to praise her in the gatherings where he spoke ill of her, in a manner appropriate for mentioning a woman who is a stranger to him, or by explaining that his anger led him to say what he did.

Fifthly: He must seek her absolution by asking for forgiveness and pardon, and admitting his mistake. If confronting her is not beneficial, then he should suffice with seeking forgiveness for her and working to rectify what he has corrupted.