Why argue what the Greek means when we are blessed with the perfect Bible in English?
SD
There is also this to consider: marriage among the 1st Century Palestinian Jews was a two-step process.
First, the couple was "betrothed," and the betrothal was normally for about one year. It roughly corresponded to our modern concept of "engagement," but there was more to it. It was employed as a custom for several reasons, notable among them was to provide time for the bride's family to amass a dowry, and for the groom (often still rather young himself) to establish himself in an occupation capable of supporting a family and household. The betrothal, however, had these unique features: the couple was considered already "married" in a legal sense when it came to inheritance rights, and the betrothal was pretty binding: a divorce would be necessary to break it (witness Joseph's dilemma when he first heard about Mary being pregnant, and he obviously knew he wasn't the father. He decided to "divorce her quietly."
The second step in the process was the actual wedding, which was an elaborate affair often taking up to a week, filled with ceremonies and festivities. The marriage proceeded at that point in ways we are culturally familiar with.
So, what has all this to do with the "porneia" controversy? Well, first, we can notice that the qualifier "porneia" only exists in Matthew's version of the Gospel, originally written in Hebrew or Aramaic for a Jewish-Christian audience. They would have been familiar with the cultural implications of their marriage process, and porneia may have come into obvious play for them because of this. Porneia can mean fornication, but it usually doesn't mean flat-out adultery. The confusion can be remedied when one considers that Jesus likely was talking about Jewish weddings to His Jewish listeners, and what He had in mind was "divorce" during the betrothal period, NOT after the actual wedding.
The parallel passages to Matthew's two uses of "porneia" (Matthew 5:32 and 19:9) can be found in Mark 10:11 and Luke 16:18. *Neither* of these passages mentions the exception of "porneia." Why? Because these two Gospels were not written for a primarily Jewish audience, the cultural situation of a two-stage marriage did not exist in thier audiences' cultres, and it was not necessary to include.
Taking all of this and wrapping it together, it seems clear enough to me that the allowed exception of "porneia" is referring to fornication (or a sort of technical adultery, since the parties are semi-married as we would think of it) committed by one of the parties in a Jewish betrothal. It has no application to any culture outside of that, and definitely no application to any Christian culture outside of the Jewish-Christians of the first Century. This is why the Catholic Church doesn't even allow the "porneia exception" as grounds for divorce. It looks to the text of Mark and Luke as normative, since the Church recognizes the irrelevancy of circumstances allowing the exception in Matthew's Gospel.
Bottom line: The porneia exception has no bearing on Christian marriages. Consummated marriages cannot be broken through divorce. Jesus meant what He said.