The Catechism in Questions & Answers

345. What does the New Testament have to say about divorce?

In the New Testament, divorce is considered a violation of the Sixth Commandment: “Therefore what God has joined together, let not man separate” (Mark 10: 9). The only exception in which divorce was permissible was in the case of adultery committed by one’s spouse (cf. Matthew 19: 9).
The New Testament’s statements concerning divorce served, above all, to improve the situation of the woman, who only had very limited rights in antiquity. The woman was thus to be protected from being arbitrarily cast aside by her husband.