You should confront him in the most private and careful way possible. See Matthew 18:15-17 and James 5:19,20. The aim is to bring back the sinner from "the error of his ways" in the most discreet way possible in order to minimize the damage to his family and reputation. Leviticus 19:17 says, "Do not hate your brother in your heart. Rebuke your neighbour frankly so that you will not share in his guilt."
I hope you have found this helpful.