The Catechism Of The Catechism Of The Catholic Church#2358

Adultery refers to marital infidelity. When two partners,of whom at least one is married to another party,have sexual relations,even transient ones,they commit adultery. Christ condemns even adultery of mere desire. The six commandment and the New Testament forbid adultery absolutely. The prophets denounce the gravity of adultery,they see it as an image of the sin of idolatry.