I have personal knowledge of one case in northern MS about 20 years ago. A young single sister confessed to an affair with a married brother. He denied it vehemently. She was disfellowshipped on the basis that it had continued for some time and she either was guilty as claimed or was a liar trying to cause someone else problems. Either way, she deserved to be disfellowshipped (according to them). Nothing happened to the brother at the time because there was no "proof." Later, it turned out he was having yet another affair, but this time there was proof. His wife divorced him, but he was disfellowshipped. I don't know if he ever confessed to the original affair.
I am long gone from there (and the Truth®), so I don't know whatever became of him. The young sister finally figured out everything she had been taught and believed all her life was a lie and she just left. Good for her!