What is the ruling regarding a young man who deceived a pious girl, promised to marry her, and borrowed a large sum of money from her, then it became clear that he is a drug addict and engaged to another, and he does not want to return the money?

If the girl has evidence that the young man took the money, she should present it to the responsible authorities to reclaim her right. If she does not have evidence, she should present the matter to her guardian or one of her mahrams to seek the help of someone who has authority over the young man to recover the money. It is permissible to supplicate against the oppressor who has not returned the money, as Allah Almighty says: "Allah does not like the public utterance of evil, except by one who has been wronged." The wronged person has been permitted to supplicate against their oppressor, but forgiveness is better. There is evidence that it is permissible to supplicate against the oppressor, even if he is a Muslim, such as the supplication of Sa'id ibn Zayd and the supplication of Sa'id ibn Jubayr, and the Prophet's (peace be upon him) warning against the supplication of the oppressed.