Catechism of the Catholic Church §2384 — excerpt
Divorce is a grave offense against the natural law. It claims to break the contract, to which the spouses freely consented, to live with each other till death.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Basil, Moralia 73, 1: PG 31, 849-852