Then you might or might not know that Porneias translated as "unchastitiy" in the NASB from Greek means more then simply "unchastity." It includes a range of sexual immorality such as incest ect, which are expressly forbidden in Lev 20:11-17 and elsewhere.
Illicit sexual practice might be a better translation but we're up against a problem with the meaning of the Greek translated into English.
However the word appears again in other parts of scripture to mean more then mere unchastity. Paul uses the word in reference to incest 1 cor 5:1, but it can mean any kind of sexual immorality.
Reference: Greek-English lexicon of the New Testament: based on semantic domains 1, 770.
Yes, πορνεία, meaning pornography, pornographic"; cf. 4205 /pórnos) which is derived from pernaō, "to sell off") – properly, a selling off (surrendering) of sexual purity; promiscuity of any (every) type.
However, that is not the meaning of the Roman Catholic usage.
Rome expands that definition.
But the term is used properly within the confines of a marriage whereby one partner is cheating on another.
Rome has said an "unlawful" marriage includes things such as no intention of having children (which would really complicate Joseph and Mary's marriage), among others.
Some of these other "unlawful" reasons include:
too young (which again would raise problems for Joseph and Mary)
no intention of being faithful(after the marriage act)
lack of form
previously married
None of those reasons are provided for in Scripture.
However the word appears again in other parts of scripture to mean more then mere unchastity. Paul uses the word in reference to incest 1 cor 5:1, but it can mean any kind of sexual immorality.
Yes, that would be what we'd call "cheating" or unfaithfulness today.
From one of Msgr Pope's articles( https://www.lifesitenews.com/opinion/jesus-rejected-unlawful-and-unchaste-marriages-in-his-own-day-heres-why-and).
Now the phrases, “unless the marriage is unlawful” and “except for unchastity,” are translations of the Greek phrase μὴ ἐπὶ πορνείᾳ (me epi porneia).
The Msgr may know his Latin, but he doesn't know his Greek.
The phrase would be properly translated "except for sexual immorality."
There is nothing in the verse to support the claim of "unless the marriage is unlawful".
Using biblegateway and a search of all English translation of Matthew 19:9 shows the NABRE is the only translation to render the passage in this manner.
The NABRE has added something to scripture not supported in the Greek texts.