This circumstance was recently featured in the NYT. The article is of note in this blog mostly because it quotes a well-known Michigan divorce attorney; Richard Roane of Grand Rapids.
With New York finally following the rest of the states in 2009, all 50-states now have "no fault" divorce laws on the books. Each state is different, however, as to how adultery, if and when proven, is factored into the divorce judgment.
The Michigan Penal Code has long-contained a chapter on adultery, defined as, "the sexual intercourse of 2 persons, either of whom is married to a third person." The scope of the criminal conduct includes divorced but cohabiting persons. The statute requires the cuckolded spouse to swear-in as the complaining witness and has a brief statute of limitation; one year.
The adultery statute merged into the penal code in 1931. The caselaw on this "consensual" crime goes back to 1884, in a case from Berrien County; People v Hendrickson. That case stands for the evidentiary proposition that the testimony of the un-married participant in an adulterous union (the "other woman") can supply the requisite testimony to support a conviction, subject of course, to cross examination.
In the here and now of 2011, Michigan's family courts have adhered to the "no-fault" provisions of the divorce statutes. Adultery is now a matter of private morals, with family court judges free to exercise their discretion regarding the weight to put on allegations of adultery and their attendant consequences in matters of child custody and property division.
State Senator Ron Jelinek has proposed legislation seeking to abolish adultery as a felony. The proposed legislation, however, has not gone anywhere since being referred to the Senate's judiciary committee shortly after its introduction in February 2009.
Occasionally, the adultery statute is cited in civil cases seeking to apply what is known as the "wrongful conduct" rule which blocks a plaintiff's attempt to gain from an adulterous relationship.
Immoral, but all too common, adultery has always posed a serious threat to the traditional family unit. Adultery, however, is a rarely charged felony. Thus, it's persistence within the penal code, particularly the anti-cohabitation provision, bloats the Michigan Compiled Laws with anachronistic provisions. Transgressions are best addressed within the discretion of the family court judges.