Is it permissible to inform a girl's parents about her relationship with a young man, and to threaten not to cease contact until they force her to become religious, based on an oath the questioner made to himself?

The fraternization of young men and women is forbidden, and evil must be denounced by advising these young people. If they do not respond, it is permissible to inform their families if that will deter them and not lead to a greater harm. This must be done purely for the sake of Allah. As for the girls, one must turn away from them and seek a righteous woman to advise them. As for the oath, expiation must be made by feeding ten poor persons, clothing them, or fasting for three days, knowing that religiosity is by choice and consent, not by compulsion.