CCC 2380 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.1 The sixth commandment and the New Testament forbid adultery absolutely.2 The prophets denounce the gravity of adultery; they see it as an image of the sin of idolatry.3
1 Cf. Mt 5:27-28.
2 Cf. Mt 5:32; 19:6; Mk 10:11; 1 Cor 6:9-10.
3 Cf. Hos 2:7; Jer 5:7; 13:27.