The Catholic Church forbids divorces, but permits an indefinite separation a mensa et toro (“from table and bed”).
There are other sayings of Jesus about divorce that prohibit it absolutely (Matt19:10 Mark 10:11-12; Luke 16:18; also1 Cor 7:10-15 Eph 5:21-33), and most scholars agree that they represent the stand of Jesus.
In Matthew 19:9, the word used is “porneia.” The problem lies in the interpretation of this word.
While some translations have “marital unfaithfulness” there are other interpretations.
*“I say to you, whoever divorces his wife (unless the marriage is unlawful) and marries another commits adultery.” * **NAB **Catholic
*“I tell you that anyone who divorces his wife, except for marital unfaithfulness, and marries another woman commits adultery.” * ** NIV **Protestant
*“And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery.” * KJV
While most Protestant Greek dictionaries define the word “porneia” as fornication or adultery, in the KJV, the Greek word “porneia” is translated as fornication, which takes place between two unmarried persons, otherwise it would be called adultery.
In the following passages the Greek word “porneia” is translated as “unchastity.”
*“For from the heart come evil thoughts, murder, adultery, unchastity, theft, false witness, blasphemy.” *
"From within people, from their hearts, come evil thoughts, unchastity, theft, murder, adultery, greed, malice, deceit, licentiousness, envy, blasphemy, arrogance, folly." NAB
Notice that both “unchastity” [porneia] and “adultery” are prohibited. Therefore, from these passages we can see that porneia does not mean adultery as that would be redundant.
Other passages in Scripture where the word “porneia” is used make it clear that it ss a reference to an unlawful and thus invalid marriage, such as where there is a close blood relationship.
Acts 15:28-29 Leviticus 17:7 Lev 17:7 Lev 17:15 Lev 18:1-6
1 Corinthians 5:1-5
As such it is a case for annulment rather than divorce. An annulment means that there never was a Sacramental marriage.