It seems, in Michigan,
Adultery is still a crime under state law, punishable by a short prison sentence, but no one has been prosecuted for the offense since 1971. Judge William B. Murphy said that first-degree criminal sexual conduct is defined as sexual penetration in the furtherance of another felony. Because adultery is a felony, he said, adulterous sex could in theory be prosecuted as rape.And in Michigan, rape can get you a life sentence.
I agree that nothing is as corrosive to a marriage than extramarital sex, but a life sentence... ? Gee!
And we thought the deep South had some repressive laws.