CCC 2365 Fidelity expresses constancy in keeping one’s given word. God is faithful. The Sacrament of Matrimony enables man and woman to enter into Christ’s fidelity for his Church. Through conjugal chastity, they bear witness to this mystery before the world.
St. John Chrysostom suggests that young husbands should say to their wives: I have taken you in my arms, and I love you, and I prefer you to my life itself. For the present life is nothing, and my most ardent dream is to spend it with you in such a way that we may be assured of not being separated in the life reserved for us. .. I place your love above all things, and nothing would be more bitter or painful to me than to be of a different mind than you.1
1 St. John Chrysostom, Hom. in Eph. 20, 8: PG 62, 146-147.