That was my thought too. Unless there was assault, coercion, or they were unable to consent I don’t see why he felt he needed to resign.
"Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God.
Simply put, a fornicator is unfit to be a pastor. The bigger skunk, however, is the evil pastor who engineered the coverup.