The seventh commandment 20:14

Adultery is sexual intercourse when one or both partners are married (or engaged, under Israelite law; cf. Deut. 22:23-29) to someone else. Adultery destroys marriage and the home, the foundations of society (cf. Matt. 5:27-28; 1 Cor. 6:9-20). Adultery is an act, not a state. People commit adultery; they do not live in adultery, except in the sense that they may continually practice it.