He writes to Ask Amy as his 20-year-old daughter visits with a boyfriend: “I have indicated that I will expect him to sleep in our guest bedroom and for our daughter to sleep in her room during his visit.
Dad, your daughter is 20. That number means she’s an adult. She doesn’t live at home. You no longer have any capability of imposing your idea of morality upon her. So, what you are asking for is for her and her boyfriend to maintain the fiction that they adhere to your idea of morality while they stay in your home. A fiction only to make you feel better as your wife, daughter, her boyfriend, and anyone who happens to visit all know the truth.
The horse is already out of the barn, and to pretend that it remains there, true to the teachings of your church, seems cowardly to me. Be brave, face the fact that your daughter is an adult, and show her that you accept that by allowing them to conduct themselves as they wish.
And it’s time to give up on the idea that the Church is the bastion of morality. To get a taste of reality, start here. That page is specific to Catholic churches, but there is no shortage of similar abuse in other Christian denominations and other religions.