Former NBA star Antoine Walker is being sued for $5 million dollars by a man who claims that Walker stole his fiancee. Kevin Jenkins says that he caught Walker and his fiancee in an "intimate moment," and confronted Walker about it. He said that Walker laughed in his face to deliberately cause him emotional distress.
Jenkins then says that he became so emotionally distressed that he thought about killing himself.
To date, I haven't heard of anyone being sued for cheating with another person's fiancee. However, I do know that in some states, you can be sued for cheating with someone else's spouse. These "alienation of affection" lawsuits are legal in several states: Hawaii, Illinois, Mississippi, New Mexico, North Carolina, South Dakota and Utah.