At islamweb.net there was something that addressed these topics, headlined with attention-grabbing "His wife and son have regular incestuous relations together."
It appears to be an advice column. From the question...
Respected Sheikh, I am a man in my late sixties and recently discovered that my 33 year old wife has regular incestuous relations with my 17 years old son.A few things to note right away: 1. Although this is not written so as to make clear she is not the biological mother of his son, I think if she was the biological mother of the son that would have been explicitly stated, which is not. 2. She is closer in age to his son than she is him. 3. Seventeen year-old males generally are bursting with hormones and constantly wanting sex. Leave one alone all day with an attractive person and... well, this isn't surprising. 4. It is entirely possible that where they live 17-year-olds can legally consent to sex with 33-year-olds.
When I confronted them they denied it, but one day I came home unexpectedly and found them in the act. They repented and promised not to do it again.So this was a matter of cheating.
I am devastated and don’t know what to do. I beg you to tell me in the light of the Quran and hadith what course of actions I shall take.This is, of course, from a Muslim website. Being cheated on, especially when the other person is another person you thought you could trust, is painful. My advice would be to seriously consider if this is unacceptable, and if he needs her to only have sex with him, if he's going to be able to treat her right going forward without going batty. If not, then the marriage should be over. But he didn't ask me. Let's get to the response was given...