There are worse situations than prostituting yourself.
by Arlieth Tralare
If you damage the relationship between you and your friend, especially with that sort of whistle-blowing, you irrevocably make it impossible to help them in the future. They will never, ever confide in you about a situation where they need confidentiality, and that damages your reputation of trustworthiness as well. And if that occurs, you won't be in a position to help any of your friends, because nobody will trust you to keep the friendship in higher regard than the issue at hand.
You need to provide an honorable alternative for them to choose instead of forcing them to submit to your judgment.