What is the Sharia ruling on how to deal with an engaged friend, after it was discovered that she continues to have an online relationship with a Christian man involving explicit conversations, and she reciprocates the same feelings, knowing that her fiancé is religious, and the questioner fears being the cause of deceiving him?

The relationship between a man and a woman who are not married is forbidden, and it is even more severe and reprehensible if it is between a Muslim woman and a non-Muslim man. You must advise this woman and explain the impermissibility of her actions, and threaten her by informing her family and fiancé if she does not stop. If she does not repent, then inform her fiancé, based on the saying of some scholars that it is obligatory to disclose the flaws of a suitor. We caution that spying on a Muslim is forbidden except in certain specific circumstances.