Catechism of the Catholic Church §1644 — excerpt
The love of the spouses requires, of its very nature, the unity and indissolubility of the spouses' community of persons, which embraces their entire life: "so they are no longer two, but one flesh."
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: FC 19