Why Not Divorce?

Because Jesus forbade it and his Word is true. Jesus is Love. Jesus is Truth. Jesus is God. Please don't shoot the messenger, but it has to be said that He, who is Truth, who is Love, forbids divorce. Divorce (i.e. 'dissolving' a genuine Christian marriage) is against God's Law. Whilst the Church is well known for emphasising careful marriage preparation as the best way of preventing divorce, many people are unaware of how sensitive the Church is to divorcees.

But Matt 5: 32 and Matt 19: 9 say that Jesus taught that divorce was acceptable in the case of adultery.

It simply would make no sense for Christ to teach that people could divorce if one or the other spouse committed adultery. All one would need do, then, if he or she wanted a divorce, would be to cheat on one's spouse. In these Bible passages Jesus is prohibiting divorce except in the case of 'porneia', a Greek word that, in this context, refers to marriages that were invalid because they were within the forbidden degrees of blood relationship (see Lev 18: 6-16) [West, C., Good News About Sex and Marriage].

Why is an amicable divorce wrong?

Because a valid marriage is joined together by God. The Holy Spirit seals the bond of matrimony until death parts the spouses. What God has joined together, man must not separate, so not even an amicable divorce is morally permissible. The indissolubility of marriage helps to protect children from the hardship, trauma and psychological scarring that follows the separation of parents. What may at first appear amicable, could end up being acrimonious in the long run.

What if one of the spouses is unfaithful to their vows?

On their wedding day, before almighty God, their witnesses, families and friends, both vowed, INDIVIDUALLY, to remain faithful 'for better, FOR WORSE … until death'. 'WORSE' encapsulates any bad stuff that might eventuate. The spouse who remains faithful to the marriage vows is left without a companion, often with children to look after. Their cross is a terrible one because Jesus expects the promises made on the wedding day to be kept until the death of the unfaithful spouse (Matt 19: 3; Mk 10: 11).

A true story might help to explain this hard teaching of Our Lord's.

Once upon a time, a newly married man (let's call him Jim) committed adultery. He deeply regretted his actions and apologised profusely, but his wife has never forgiven him. Consider the horrendous betrayal that Jim's faithful wife suffered as a result of his infidelity. She was cheated upon and has never forgiven her husband Jim for what he did to her. Jim waited a long time for his wife to take him back. He begged her to take him back if only for the sake of their two children. Jim's wife refused. Today, they live separate lives on opposite ends of the country. Both still go to Sunday Mass. Jesus teaches faithfulness; Jim was not faithful. He has ended up living with another woman. Jesus teaches forgiveness; Jim's wife has never forgiven him. She has remained faithful to her marriage vows but is tortured by the betrayal that she cannot forgive. Once a month, Jim has custody of his two beautiful daughters whom he had with his lawfully wedded wife. He sees them over a weekend. He takes them to Mass. He is living with another woman now. He knows that he cannot receive Holy Communion because he is living a life contrary to the Gospel. One Sunday, an old school friend of Jim's, who knows of his current de-facto relationship, saw him taking his daughters to Mass. His friend asked: "Why are you frequenting a Church that forbids you from receiving Communion?" Jim responded: "I want to give my daughters the best I can. Catholicism is the best I can give them. I let them and their mother down. Why should I expect the Church to change a law that I broke?"

Jesus knows better than anyone the devastation caused by people not keeping their promises. But, the fact that some people break the marriage laws of the Church does not mean that they should be changed. Jesus prohibits divorce (and re-marriage when the lawfully wedded spouse still lives) also because of the disorder it brings into the family and society [CCC 2382 - 2386].

References:
NB Don’t confuse separation due to abuse with divorce / re-marriage. Also, civil divorce can be morally permissible if it is the only way of ensuring certain legal rights. Marriage law is complex and advice from a priest in good standing with the Church is recommended. For further reading, see Kippley, J, Marriage Is for Keeps; Robinson, G. Marriage, Divorce & Nullity

* Please note that this text should be read in the context of the whole work and in recognition of the appropriate paragraphs of the Catechism of the Catholic Church highlighted in the index.