“Why is the Church against divorce? Isn’t it better than being in an unhappy marriage?” These are two common questions asked by those who do not see marriage as a life-ling endeavor. First, The Church is not completely against separation and divorce. Catechism of the Catholic Church (CCC) paragraph 2383 states, “The separation of spouses while maintaining the marriage bond can be legitimate in certain cases provided for by canon law. If civil divorce remains the only possible way of ensuring certain legal rights, the care of the children, or the protection of inheritance, it can be tolerated and does not constitute a moral offense.” However, a civil divorce cannot break the marriage bond (cf. CCC para. 2382). In Mt 19:4-6, regarding marriage, Jesus says, “What therefore God has joined together, let no man put asunder.” Marriage between man and woman symbolizes Jesus’ marriage to the Church. In light of this teaching, it is unthinkable that Jesus would ever divorce his bride and take another. The eternal plan to create his bride and consummate his relationship with her on the cross, can never be abrogated. Thus, valid marriages can never be abrogated.
Regarding happiness, the Church understands that true happiness is not found in a broken household of any kind. It is first found in love towards God and then love towards neighbor. Within neighborly love, marital love takes a primary place. Marital love, according to Humanae Vitae, is fully human in that it is an act of the free will by which man and woman freely give themselves to one another and grow in holiness as one heart and soul. It is total in that husband and wife share everything, including themselves. It is faithful and exclusive in that fidelity and exclusivity express authentic marital love. Finally, it is fruitful in that marital and conjugal love are always directed toward the procreation and education of children, who are the supreme gift of marriage.
Still, someone could argue that not everyone has this understanding of marriage and, therefore, may enter a marriage prematurely. A contract (or covenant) entered into prematurely, however, is still a contract provided it is freely agreed upon by both parties who are of proper age and sound mind. Free will, a promise (except for impediments defined by the Church), and consummation are what make the marital covenant binding. When one makes this promise prematurely, it merely means the promise is made with haste or without a complete knowledge of what marriage entails. Regardless, both parties promised themselves to one another until death. Thus, both husband and wife must work, in love, to make their marriage a happy one and one suitable for their children.
In the event of civil divorce, one can seek a declaration of nullity from the Church. Annulments, as they are commonly called, are not Church divorces. Rather, they are Church investigations into the validity of marriages. If the Church finds that impediments to the marriage exist, a Declaration of Nullity is issued. If there are no impediments, the marriage remains valid, regardless of civil actions.
 Robert L. Fastiggi. What the Church Teaches About Sex (Out of print – Available as a PDF).