What the Catechism says about both indissolubility and infallibility....

We need to understand what the Catechism says about both indissolubility and infallibility:

•  889 In order to preserve the Church in the purity of the faith handed on by the apostles, Christ who is the Truth willed to confer on her a share in his own infallibility. By a "supernatural sense of faith" the People of God, under the guidance of the Church's living Magisterium, "unfailingly adheres to this faith."⁴¹⁷
• 890 The mission of the Magisterium is linked to the definitive nature of the covenant established by God with his people in Christ. It is this Magisterium's task to preserve God's people from deviations and defections and to guarantee them the objective possibility of professing the true faith without error. Thus, the pastoral duty of the Magisterium is aimed at seeing to it that the People of God abides in the truth that liberates. To fulfill this service, Christ endowed the Church's shepherds with the charism of infallibility in matters of faith and morals. The exercise of this charism takes several forms:
• 891 "The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office, when, as supreme pastor and teacher of all the faithful - who confirms his brethren in the faith he proclaims by a definitive act a doctrine pertaining to faith or morals. . . . The infallibility promised to the Church is also present in the body of bishops when, together with Peter's successor, they exercise the supreme Magisterium," above all in an Ecumenical Council.⁴¹⁸ When the Church through its supreme Magisterium proposes a doctrine "for belief as being divinely revealed,"⁴¹⁹ and as the teaching of Christ, the definitions "must be adhered to with the obedience of faith."⁴²⁰ This infallibility extends as far as the deposit of divine Revelation itself.⁴²¹
• 1610 Moral conscience concerning the unity and indissolubility of marriage developed under the pedagogy of the old law. In the Old Testament the polygamy of patriarchs and kings is not yet explicitly rejected. Nevertheless, the law given to Moses aims at protecting the wife from arbitrary domination by the husband, even though according to the Lord's words it still carries traces of man's "hardness of heart" which was the reason Moses permitted men to divorce their wives.¹⁰¹
• 1611 Seeing God's covenant with Israel in the image of exclusive and faithful married love, the prophets prepared the Chosen People's conscience for a deepened understanding of the unity and indissolubility of marriage.¹⁰² The books of Ruth and Tobit bear moving witness to an elevated sense of marriage and to the fidelity and tenderness of spouses. Tradition has always seen in the Song of Solomon a unique expression of human love, insofar as it is a reflection of God's love - a love "strong as death" that "many waters cannot quench."¹⁰³
• 1615 This unequivocal insistence on the indissolubility of the marriage bond may have left some perplexed and could seem to be a demand impossible to realize. However, Jesus has not placed on spouses a burden impossible to bear, or too heavy - heavier than the Law of Moses.¹⁰⁸ By coming to restore the original order of creation disturbed by sin, he himself gives the strength and grace to live marriage in the new dimension of the Reign of God. It is by following Christ, renouncing themselves, and taking up their crosses that spouses will be able to "receive" the original meaning of marriage and live it with the help of Christ.¹⁰⁹ This grace of Christian marriage is a fruit of Christ's cross, the source of all Christian life. 
• 1643 "Conjugal love involves a totality, in which all the elements of the person enter - appeal of the body and instinct, power of feeling and affectivity, aspiration of the spirit and of will. It aims at a deeply personal unity, a unity that, beyond union in one flesh, leads to forming one heart and soul; it demands indissolubility and faithfulness in definitive mutual giving; and it is open to fertility. In a word it is a question of the normal characteristics of all natural conjugal love, but with a new significance which not only purifies and strengthens them, but raises them to the extent of making them the expression of specifically Christian values."¹⁵²
• 1644 The love of the spouses requires, of its very nature, the unity and indissolubility of the spouses' community of persons, which embraces their entire life: "so they are no longer two, but one flesh."¹⁵³ They "are called to grow continually in their communion through day-to-day fidelity to their marriage promise of total mutual self-giving."¹⁵⁴ This human communion is confirmed, purified, and completed by communion in Jesus Christ, given through the sacrament of Matrimony. It is deepened by lives of the common faith and by the Eucharist received together.
• 1645 "The unity of marriage, distinctly recognized by our Lord, is made clear in the equal personal dignity which must be accorded to man and wife in mutual and unreserved affection."¹⁵⁵ Polygamy is contrary to conjugal love which is undivided and exclusive.¹⁵⁶
• 1647 The deepest reason is found in the fidelity of God to his covenant, in that of Christ to his Church. Through the sacrament of Matrimony the spouses are enabled to represent this fidelity and witness to it. Through the sacrament, the indissolubility of marriage receives a new and deeper meaning.
• 2035 The supreme degree of participation in the authority of Christ is ensured by the charism of infallibility. This infallibility extends as far as does the deposit of divine Revelation; it also extends to all those elements of doctrine, including morals, without which the saving truths of the faith cannot be preserved, explained, or observed.⁷⁷
• 2051 The infallibility of the Magisterium of the Pastors extends to all the elements of doctrine, including moral doctrine, without which the saving truths of the faith cannot be preserved, expounded, or observed. 
•  2364 The married couple forms "the intimate partnership of life and love established by the Creator and governed by his laws; it is rooted in the conjugal covenant, that is, in their irrevocable personal consent."¹⁴⁷ Both give themselves definitively and totally to one another. They are no longer two; from now on they form one flesh. The covenant they freely contracted imposes on the spouses the obligation to preserve it as unique and indissoluble.¹⁴⁸ "What therefore God has joined together, let not man put asunder."¹⁴⁹