What many Christians conclude, is that Jesus was saying a valid marriage can be dissolved if one or both spouses commits “porneia”.
Many studies have been undertaken over the “exception clauses” in Matthew 5 and 19, and various interpretation can be made from these passages.
The term “porneia” is Greek, and can mean a variety of things, depending on context.
It can be translated as Sexual Immorality, prohibited sexual relations, Fornication, Prostitution…
What seems to be the crux of major disagreement with most non-Catholic Christians and Catholic Christians is this:
Those who believe Matthew used “porneia” as an act referring to adultery are opposed to Catholic Teaching.
The illogic of this interpretation is that, if this was true, Jesus would have used the term for adultery in the so called exception clause. Here is why… even if “porneia” means infidelity or sexual immorality, if it happens in a valid marriage, it must be called adultery! But if it happens outside of Holy Matrimony, then it gives cause for civil divorce and Holy Matrimony never occurred.