Seven states have an "alienation of affection" law in the U.S. The law basically says that a spouse can sue a third party for claiming to interfere with their marriage due to infidelity.
Most of the states that have this ancient law won't change the law, because the legislature doesn't want to be known for legalizing adultery.
The law originally was created when wives were seen as property.
If a man took her from her husband, the husband could sue for loss of property through the alienation of affection law. Today, both men and women exercise the law.
However, if taken to court, the people involved have to be ready for all their dirty laundry to be displayed. It can be extremely humiliating for all parties.
In 2010, Cynthia Shackelford of North Carolina won a $9 million lawsuit against Anne Lundquist, her husband's mistress under the alienation of affection law. She stated that she did it to send a message to other women to think before trying anything with a married man and ruining his family.