The NAB was not translated by ICEL but had its own translators. Also the Jerusalem Bible and the RSV-CE retain the more traditional translation. Below is apretty good summation of Catholic teaching and opinion.
Did Jesus Say Adultery Is Grounds for Divorce?
By Jimmy Akin
In the first-century Mediterranean world, divorce and remarriage were common—except among the Jews. Jesus in particular used strong language in condemning the practice. In Matthew 5:31-32, he says, "It was also said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’ But I say to you that every one who divorces his wife, except on the ground of unchastity, makes her commit adultery; and whoever marries a divorced woman commits adultery." Similarly, in Matthew 19:9, he says, "And I say to you: Whoever divorces his wife, except for unchastity, and marries another, commits adultery" (emphases added).
Many Protestants seize on these so-called "exceptive clauses" as legitimizing divorce in cases where one of the spouses has committed adultery or engaged in some sort of sexual sin.
There are a number of problems with this. First among them is that the exceptive clauses do not appear in the parallel passages in Mark and Luke. In Mark 10:11-12, Jesus says only, "Whoever divorces his wife and marries another, commits adultery against her; and if she divorces her husband and marries another, she commits adultery." Likewise, Luke 16:18 says, "Every one who divorces his wife and marries another commits adultery, and he who marries a woman divorced from her husband commits adultery."
This is striking. How could Mark and Luke, writing for the Greco-Roman world, omit the one, glaring exception that allows remarriage after divorce? Adultery and sexual sins were rampant in the Roman culture. Mark and Luke would have realized that their audiences needed to know about the exception even more than the Jewish audience for which Matthew wrote.
The exceptive clauses also do not appear in Paul’s discussion of divorce and remarriage. In Romans 7:2-3, he writes that "a married woman is bound by law to her husband as long as he lives; but if her husband dies she is discharged from the law concerning the husband. Accordingly, she will be called an adulteress if she lives with another man while her husband is alive. But if her husband dies she is free from that law, and if she marries another man she is not an adulteress."
And in 1 Corinthians 7:10-11, 39, he writes, "To the married I give charge, not I but the Lord, that the wife should not separate from her husband (but if she does, let her remain single or else be reconciled to her husband)—and that the husband should not divorce his wife. . . . A wife is bound to her husband as long as he lives. If the husband dies, she is free to be married to whom she wishes, only in the Lord."
Paul was dealing also with a Greco-Roman audience, and he also does not make an exception for unfaithfulness or sexual sin. (The only exception he does make is for the dissolution of a non-sacramental marriage when one spouse has converted to Christianity [1 Cor. 7:12, 15]—what we know today as the Pauline privilege—but that is a different matter.)
Because the exceptive clauses occur only in Matthew’s Gospel—one written for a Jewish audience—it suggests that they reflect some issue of particular concern to Jews. What might this be?
One possibility is that the exceptive clauses are there as an illustration of the precision demanded in rabbinic logic. In other words, the clauses indicate that if one divorces an adulterous wife, one isn’t making her into an adulteress because she already is one. That doesn’t mean that she’s free to remarry; it just means that you aren’t forcing her into an adulterous situation if you divorce her.
Another possibility is that the exceptive clauses are a way of avoiding altogether the subject of an unchaste spouse. In Judaism around this period, there was a debate between the school of Hillel and the school of Shammai over the circumstances in which one could divorce. The Hillelites argued that it could be essentially for any reason, while the Shammaites argued it could be only for adultery. The exceptive clauses could be a way of avoiding this debate. The Greek grammar allows the passage to be understood roughly in this sense: "Whoever divorces his wife and marries another—I’m not going into the subject of unchastity—commits adultery."
A third possibility is that the Greek term used for "unchastity"— porneia—is being used in a special sense. For example, some have taken it to refer to unchaste behavior before the marriage is consummated. At that point, it is possible to dissolve the marriage, for marriages become indissoluble only when they are consummated.
Today, with the tradition of the wedding night, it is highly unlikely a spouse could be unfaithful between the marriage ceremony and the consummation. However, in Jesus’ time it was customary for a couple to be legally married for about a year before the consummation. The bride continued to live with her family while the husband prepared their home. At the end of this time there was the "fetching of the bride" ceremony, where the groom took her back to his own home with family and friends accompanying them. Then, during the wedding party, the couple would retire and consummate their union. Clearly, within this long time frame unchastity was possible on the part of one of the spouses.
Why would Matthew be the only Evangelist to point out the possibility of dissolving such unions? Because he is the only one who mentions that, when Mary was discovered to be with child by the Holy Spirit, Joseph had in mind to divorce her quietly (Matt. 1:19). He alone would seem to have a reason to clarify why Joseph’s planned course of action was legitimate, given what Jesus said later regarding marriage.
Others have interpreted the Greek term used for "unchastity"— porneia—as a reference to incest, the idea being that divorce and remarriage is permissible in the case of incestuous marriages, since the marriage was never valid to begin with. If this is correct, then we have the principle that underlies modern annulments: Those who are not validly married are free to contract it.
Advocates of this interpretation point out that porneia is not the usual Greek term for adultery. Indeed, in the passages cited above, Jesus uses the term for adultery (moicheia) and does not identify it with porneia. These advocates point out also that many peoples in the eastern-Mediterranean region had marriage practices that allowed unions forbidden by Leviticus 18. This caused problems when individuals wanted to convert to Judaism and Christianity. Did they have to leave their spouses? Matthew, writing in an eastern-Mediterranean context, would have had reason to insert a clarification to prevent such converts from using the unqualified statement as justification for staying with their current spouses.
The idea that porneia is being used in this narrow way is suggested by two other biblical passages. In Acts 15:29, it is proposed that, to avoid offending Jewish believers, Gentile converts abstain from eating idol meat, blood, strangled animals, and from porneia. These objections are often regarded as being based directly on Leviticus 17-18, where the same things are prohibited in the same order.
The second passage is 1 Corinthians 5:1, where Paul applies the word porneia to the case of a man who has married his stepmother—a case forbidden by Leviticus 18:8. These considerations make it reasonable to assume that porneia is being used in the exceptive clauses to refer to incestuous unions.
Whichever above arguments you find convincing, it is clearly false that Jesus meant to allow divorce and remarriage when one party has committed adultery. Matthew 19:9 has often been read against the context of the Hillel-Shammai debate and interpreted to mean that Jesus was simply siding with Shammai in permitting divorce only for adultery. But this does not square with two key points in the text.
First, 19:3 specifically says that the Pharisees were trying to test Jesus, and it uses a Greek word—peirazo—that the synoptic Gospels use to indicate an act of malice. Even John P. Meier, a biblical liberal, notes, "If the Pharisees are simply asking Jesus he favors the opinion of Hillel or Shammi, how does this constitute a malicious attempt to force him into a dilemma whereby one choice or either choice would involve a damaging statement? After all, both rabbinic opinions were perfectly respectable" (The Vision of Matthew, 252).
Second, Jesus’ answer is so amazing that in 19:10 the disciples declare that it would be better not to marry if what Jesus has said is true. Meier again: "This is not a reaction to the well-known position of Shammai, which would hardly lead a Jew or anyone else to such a conclusion. Matthew has the disciples react all too humanly to Jesus’ total prohibition of divorce" (ibid., 253).
Finally, "if Matthew were espousing adultery as grounds for divorce, he would soon run up against grave practical difficulties. In this hypothesis, Matthew would allow divorce and remarriage for a husband and wife who had committed adultery. But a husband and wife who remained faithful to each other would not be allowed to divorce; indeed their attempt at divorce would be considered adultery. Obviously, the only thing to do for a faithful Christian couple who wanted a divorce would be to commit adultery, after which a dissolution of the marriage would be allowed. What we wind up with is divorce on demand, with a technical proviso of committing adultery. This all constitutes a strange church discipline, one in which adultery seems encouraged and fidelity discouraged" (ibid.).
The situation Meier describes is actually found in many Protestant churches. Any experienced Evangelical counselor can attest that many Evangelicals who find themselves in difficult marital situations do commit such sins specifically for purposes of being able to divorce and remarry. They may say to themselves, "Jesus will forgive me afterwards" or "I have already been forgiven for all my sins—future ones included." Through this loophole Evangelicalism has absorbed the secular world’s divorce and remarriage ethic, just as it has absorbed the secular world’s contraceptive mentality.
Fortunately, in recent years all the interpretive options mentioned above have found advocates in conservative Protestant circles. Time will tell whether this new recognition of the seriousness of Jesus’ teaching on divorce and remarriage will bear significant fruit.