What are the disadvantages of this relationship and its impact on one's faith and soul, and what are the compelling reasons for ending it, along with practical steps for doing so, especially after learning that the other party is married?

The prohibition of such relationships is clear, and it is a sin that one dislikes people becoming aware of, as the Prophet, peace and blessings be upon him, said: "Sin is what wavers in your heart and you dislike people finding out about it." Its drawbacks include: committing the forbidden, which blackens the heart; a bad reputation for the girl if it becomes exposed; and it may lead to even greater sins. There is no need for gradualism in abandoning it; rather, it must be severed immediately in response to the command of Allah and His Messenger, as in His, the Almighty's, saying: "It is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should [thereafter] have any choice about their affair." The fact that the young man is married means injustice to his wife and children, and usurping their rights from him, and it may be a cause of spoiling his relationship with his family. Therefore, the relationship must be severed immediately, and one should occupy oneself with beneficial deeds such as prayer, remembrance of Allah (dhikr), and supplication (du'a).