|St. Augustine and the Fire of Wisdom|
"This problem often arises: if a man and a woman live together without being legitimately joined. not to have children but because they could not observe continence; and if they have agreed between themselves to have relations with no one else, can this be called a marriage?
Perhaps, but only if they have resolved to maintain until death the good faith that they had promised to themselves, even though this union did not rest on a desire to have children." The Good of Marriage 5, 5