As human beings, we are comprised of both spirit and body. Thus, the bond of marital love is ordered to a complete fidelity in both of these aspects.
Faithfulness in the Spirit
In marriage, man and wife are called to be faithful to each other in their thoughts and in their words. They should always take into account the dignity of the beloved, and this means that they are called to avoid becoming personally overcome with any grievous feelings with the one they love. Throughout the years, it is certain that man and wife will encounter obstacles in their marriage (both big and small). However, a true testimony to authentic marital love is a union that withstands these obstacles and burdens, remaining faithful, especially when love is put to the test.
Marital love requires always willing the good of the beloved, and this begins first in the mind. The way one thinks about their spouse and handles interactions with them is extremely important. In marital love, both spouses are given the great gift of unity, and that unity requires cultivation and nurturing. If the mind and heart are not willing to see the beauty of the other soul (especially in difficult times and moments), it will be incredibly difficult for love to flourish. When faced with confrontations and disagreements, both spouses should always work on ridding themselves of feelings of resentment, interior aversions, and unjust anger, always remaining faithful in spirit to their spouse, ready to communicate and give the other the benefit of the doubt.
Also, man and wife are called to temper their inner passionate desires. Impure desires begin in thoughts, and require proper ordering. When they are not properly ordered, the object of love will quickly turn into utility, lustfulness, and even infidelity. Both spouses must always remember each other’s dignity, and never treat the other as an object to be used, lusted after, or discarded for another. Healthy sexual desire is a great thing, but when it is removed from the inherent purpose of sex (i.e. for unity and procreation)–even in thoughts–the object becomes a distorted and false image of love. Anything less than the authentic expression of love (that it is free, total, faithful, and fruitful), is in essence, infidelity in our calling to love as God loves.
Entertaining impure thoughts, in whatever form, robs the spouses of the ability and readiness to deny themselves for the sake of their beloved, and it denies each spouse of their dignity in order to satisfy lust. Fidelity in marriage calls for fidelity in the mind, and living in the world of fantasy is merely a means of escape from reality and the demands of authentic human love.
Faithfulness in Body
With regards to faithfulness of the body, it is important to remember the inherent purpose of human sexuality. Sex is a gift given by God, and it is the means by which the wedding vows become flesh. Thus—since it is the physical expression of the invisible, unbreakable bond between man and wife—it should not be separated from this union in any way.
This is why complete fidelity of the body is essential in marriage. Our world tells us that we need to constantly be looking to fulfill our sexual “needs,” but sexuality is meant to be a gift between man and wife alone. When the inherent purpose is removed from the act, it ceases to be a real gift. For example, both adultery and masturbation are acts primarily focused on the “I” (i.e. selfish desires) rather than the “we” (man and wife, united in love in marriage). In each of these examples, the gift of sexuality is misused for the sake of selfish and lifeless pleasure.
Lifelong Commitment to Fidelity
As Alice Von Hildebrand once said, “Marriage is a great thing: the most complete, the most intense, the most beautiful relationship possible between two human beings.” As such, marriage calls for lifelong unfailing loyalty, and requires consistent practice and dying to self—regardless of extenuating circumstances. It is through complete fidelity in marriage that two people are able to grow together, and offer a mutual gift of self to one another.