Why does the Catholic Church teach that there is no divorce under any circumstance even when the Scriptures allow divorce in case of Adultery(Matthew 5:31-32 and Matthew 19:3-9)

 This is has been a controversial topic especially between Catholics and Protestants for many many years.  The verses which are normally discussed and debated by both camps are Matthew 5:31-32 and Matthew 19:3-9.

Matthew 5

31 “It has been said, ‘Anyone who divorces his wife must give her a certificate of divorce.’[a] 32 But I tell you that anyone who divorces his wife, except for sexual immorality, makes her the victim of adultery, and anyone who marries a divorced woman commits adultery. AKJV

Matthew 19

8 Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning. 9 I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery.”

Other versions in place of sexual immorality translate it as adultery or fornication. 

In most discussions or writings on this issue the focus is on one spouse committing adultery or sexual immorality with someone else outside their marriage. However these verses actually point to the relationship between the man and woman living together. It is not talking about infidelity of one spouse to another, it is actually talking about the validity of the marriage between those two spouses. To be precise, these verses are pointing to an adulterous situation where a man and a woman live together without a valid marriage and this is the only exception where one is allowed to divorce. 

Validity of A Marriage 

To actually deal with this topic let us deal with the issue of the validity of marriage. It is possible that A man and a woman can live together as husband and wife but without a valid marriage and especially in the modern world the validity of a marriage is not taken serious. They are many reasons why a marriage can be invalid for example 

1. getting married out of compulsion by other people, 

2. entering marriage without the intention to live together as husband or wife of only one spouse forever,  

3. A person has not reached the age of reason to consent to marriage. etc etc

From the discourse between Jesus and the woman at the well it is clear that the woman actually knew that the man she is living with is not actually his husband. 

John 4

17 The woman answered, and said: I have no husband. Jesus said to her: Thou hast said well, I have no husband:

18 For thou hast had five husbands: and he whom thou now hast, is not thy husband. This thou hast said truly.

In this case the woman actually lived with a man who is not married to her knowing fully. Meaning she actually knew she was living in an adulterous marriage. They are also instances that a person can live with a spouse without knowledge that they are not truly married but still it is an adulterous marriage. Such can be a case where people do not even know what constitutes a valid or invalid marriage.

Despite whether one knows he or she is living in an adulterous marriage or not, this is the only exception where divorce is actually allowed. 

If the cheating of one spouse can be a reason for divorce, it means its easy for people to get divorces. However such is not case according to the Scriptures because even the disciples acknowledge that the case is difficult to the extent that they said it is better not to marry if you cannot put away your validly married wife or husband(Matthew 19:10). If a cheating spouse is the reason for divorce, then it goes against our Lord 's teaching that what God has joined together no man shall separate and this includes the spouses in that marriage. A spouse who no longer has feelings or no longer "love"  the other spouse can simply cheat so that the other partner can just issue a divorce.

Matthew 19

4 He said in reply, “Have you not read that from the beginning the Creator ‘made them male and female’

5 and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’?

6 So they are no longer two, but one flesh. Therefore, what God has joined together, no human being must separate.”

This interpretation that divorce is only allowed for those with invalid marriages is also supported by the NAB translation of the Bible which specifically points us to the same thing using the term unlawful instead of invalid:

Matthew 5

31* “It was also said, ‘Whoever divorces his wife must give her a bill of divorce.

32 But I say to you, whoever divorces his wife (unless the marriage is unlawful) causes her to commit adultery, and whoever marries a divorced woman commits adultery.

Matthew 19:

9 I say to you,* whoever divorces his wife (unless the marriage is unlawful) and marries another commits adultery.”

10 [His] disciples said to him, “If that is the case of a man with his wife, it is better not to marry.”

Once a two are validly married they cannot be separated. Whoever marries anyone who separates themselves from a valid marriage commits adultery.

Paul summarizes all these in 1 Corinthians 7

10 To the married, however, I give this instruction (not I, but the Lord):* A wife should not separate from her husband

11—and if she does separate she must either remain single or become reconciled to her husband—and a husband should not divorce his wife.