score:6
The cessation of sexual acts between a married couple by common consent is seen as valid by the Church, particularly as they age. Also, the ancient interpretation (demonstrated by the Canons of the Councils of Carthage) is that upon raising a man to the diaconate (and, of old, presbyterate and episcopate) they must maintain perfect continence, that is, must cease sexual activity with their wives, if they have any.
That being said, the Catechism teaches:
The openness to fertility
1652 "By its very nature the institution of marriage and married love is ordered to the procreation and education of the offspring and it is in them that it finds its crowning glory."Gaudium et Spes 48 #1; 50
Children are the supreme gift of marriage and contribute greatly to the good of the parents themselves. God himself said: "It is not good that man should be alone," and "from the beginning (he) made them male and female"; wishing to associate them in a special way in his own creative work, God blessed man and woman with the words: "Be fruitful and multiply." Hence, true married love and the whole structure of family life which results from it, without diminishment of the other ends of marriage, are directed to disposing the spouses to cooperate valiantly with the love of the Creator and Savior, who through them will increase and enrich his family from day to day.GS 50 #1; cf. Gen 2:18; Mt 19:4; Gen 1:28
1653 The fruitfulness of conjugal love extends to the fruits of the moral, spiritual, and supernatural life that parents hand on to their children by education. Parents are the principal and first educators of their children.Cf. Gravissimum Educationis 3 In this sense the fundamental task of marriage and family is to be at the service of life.Cf. Familiaris Consortio 28
1654 Spouses to whom God has not granted children can nevertheless have a conjugal life full of meaning, in both human and Christian terms. Their marriage can radiate a fruitfulness of charity, of hospitality, and of sacrifice.
1664 Unity, indissolubility, and openness to fertility are essential to marriage. Polygamy is incompatible with the unity of marriage; divorce separates what God has joined together; the refusal of fertility turns married life away from its "supreme gift," the child (GS 50 # 1).
In other words, though a couple need not have sexual relations constantly through their lives, they must make an honest effort, particularly in the beginning of their conjugal life, to open themselves to fertility and receive any children which the Creator has prepared for them. A Catholic who marries with no intention of ever having children does not marry validly, but once children have come or old age or the Diaconate have rendered unlikely or impossible their arrival, a couple may agree to end sexual relations without prejudice to their matrimony, provided they keep "radiat[ing] a fruitfulness of charity, of hospitality, and of sacrifice."
Upvote:3
No, sexual relations are not essential to marriage. Thus, absence of sexual relations does not mean there is no marriage. Marital consent is what makes a marriage, although sexual relations consummate a marriage.
St. Thomas Aquinas discusses in his Summa Theologica suppl. q. 64 a. 6 the question of "Whether husband and wife can take a vow contrary to the marriage debt without their mutual consent?" The implication is that it is permissible as long as there is mutual consent. This follows from 1 Cor. 7:5:
Defraud [deprive] not one another [of sexual relations], except, perhaps, by consent, for a time, that you may give yourselves to prayer; and return together again, lest Satan tempt you for your incontinency.
St. Paul councils to "return together again" in case husband and/or wife become tempted against purity.
Cappello, S.J., Tractatus Canonico-Moralis de Sacramentis. Vol V. De Matrimonio, p. 805 (quoted in McAuliffe, Catholic Moral Teaching on the Nature and Object of Conjugal Love p. 77):
Neither spouse per se is bound to seek the debitum, because no one is bound to use a thing which is a right. … Per accidens, however, such an obligation can exist, especially in the husband … if the use of matrimony is necessary to foster love or to avoid disagreements.
Neuter conjux per se tenetur petere debitum, quia nemo tenetur uti jure suo. Per accidens autem potest adesse obligatio petendi, praesertim in viro … si usus matrimonii necessarius est ad fovendum amorem vel ad dissidia avertenda.
In vol. 7 of The Great Commentary (pp. 130-1) by Fr. Cornelius à Lapide, S.J., which is on 1 Corinthians, commentating specifically on 1 Cor. 7, Fr. Cornelius collects a list of 13 married saints and others who remained 100% continent in their marriages. Some prominent examples are Saints Mary & Joseph and St. Cecilia and Valerian.