Since I am uncomfortable with immorality as potentially too broad a translation of πορνεία I’ll treat it like an unknown X.  So if I remove X from the equations so to speak I get a clearer view of Jesus’ meaning without X.  I might even gain some insight into ways to solve for X where X = πορνεία.

So there are two statements in Matthew 5:32 (NET): 1) everyone who divorces his wife makes her commit adultery (μοιχευθῆναι, a form of μοιχεύω), and 2) whoever marries a divorced woman commits adultery (μοιχᾶται, a form of μοιχάω).  There is one statement in Matthew 19:9 (NET): 3) whoever divorces his wife and marries another commits adultery (μοιχᾶται, a form of μοιχάω).  So I have three statements made by Jesus about divorce and adultery.  The missing statement from Matthew 19:9 in the NET is not particularly relevant to this consideration because it was identical to statement 2) in Matthew 5:32 (NET).

With this as a baseline I’ll put X back in to see what is changed by X.

What is fairly clear now is that the introduction of X did not alter the fact that the man divorced his wife in Matthew 5:32 (NET).  It did not change the facts that Moses permitted you to divorce your wives because of your hard hearts, nor that from the beginning it was not this way.¹  The introduction of X has absolutely no bearing on the facts that from the beginning the Creator made them male and female [see Addendum below], and said, ‘For this reason a man will leave his father and mother and will be united with his wife, and the two will become one flesh’ [see Addendum below]?  So they are no longer two, but one flesh.  Therefore what God has joined together, let no one separate.²

The only facts available for alteration by X or the facts pertaining to adultery if/when a woman so divorced remarries.  I’m going to assume that X in this case was the husband’s doing.  When a wife is divorced because of the husband’s X, Jesus does not consider her remarriage adultery, not for her, not for the man who marries her.  Likewise in Matthew 19:9 (NET) Jesus does not consider the husband’s remarriage adultery if the wife does X.  And by no means, in either case, is it a command to divorce over X.  Forgiveness, mercy, love and grace remain the standing order of the day.

My advice to anyone who, like me, is caught up in a divorce is to stop looking to rules like this to justify yourself.  But if we confess our sins, he is faithful and righteous, forgiving us our sins and cleansing us from all unrighteousness.  If we say we have not sinned, we make him a liar and his word is not in us.³  Jesus told of a man who stood far off and would not even look up to heaven, but beat his breast and said, ‘God, be merciful to me, sinner that I am!’  I tell you that this man went down to his home justified…⁴

The one who confesses divorce as sin and receives mercy, forgiveness and justification from God through Jesus Christ is free to marry again as the Lord leads.  The one who justifies divorce by laws, rules or principles disagrees with God through Jesus Christ, does not receive God’s mercy, forgiveness or justification, but relies on his own righteousness derived from the law.  If this one remarries after divorce it is adultery in Jesus’ eyes.  But all is not lost.  …if we confess our sins, he is faithful and righteous, forgiving us our sins and cleansing us from all unrighteousness.  If we say we have not sinned, we make him a liar and his word is not in us.  Jesus told of a man who stood far off and would not even look up to heaven, but beat his breast and said, ‘God, be merciful to me, sinner that I am!’  I tell you that this man went down to his home justified…

Addendum: September 8, 2021
According to a note (6) in the NET Matthew 19:4b is a quotation of Genesis 1:27b and 5:2a.  Tables comparing the Greek of Jesus’ quotation with that of the Septuagint follow.

According to a note (7) in the NET Matthew 19:5 is a quotation of Genesis 2:24.  A table comparing the Greek of Jesus’ quotation with that of the Septuagint follows.

A table comparing Genesis 5:2 in the Tanakh, KJV and NET, and a table comparing the Greek of Genesis 5:2 in the Septuagint (BLB and Elpenor) follow.