An adulterous relationship is a sexual relationship between a married person and someone they are not married to. An adulterous person is someone who commits adultery.
英英词典释义
Adjective
1. characterized by adultery;
"an adulterous relationship""extramarital affairs""the extracurricular activities of a philandering husband"
2. not faithful to a spouse or lover;
"adulterous husbands and wives""a two-timing boyfriend"