The Catechism of the Catholic Church (1994):
2391 Some today claim a "right to a trial marriage" where there is an intention of getting married later. However firm the purpose of those who engage in premature sexual relations may be, "the fact is that such liasons can scarcely ensure mutual sincerity and fidelity in a relationship betwen a man and a woman, nor, especially, can they protect it from inconstancy of desires or whim." Carnal union is morally legitimate only when a definitive community of life between a man and woman has been established. Human love does not tolerate "trial marriages." It demands a total and definitive gift of persons to one another.