Exactly, so neither he or she were free to marry.
Moral cleanness is indelibly stamped upon hundreds of pages of Luther's writings
What does it have to do with him fornicating with a nun? Or are you denying this historical fact?
It's not called FORNICATION when you are married to each other before God! Are you denying a BIBLICAL fact??? Both Luther and his wife LEFT the false religious system of Roman Catholicism - just as many STILL do today. These people are not slaves to a system they no longer accept. Better that they leave and get married to each other than sneak around and fornicate while still in a clerical system that demands celibacy (i.e., Pope Julius II, Pope Paul III, Pope Pius IV, Pope Sergius III, Pope John X, Pope John XII, Pope Alexaner VI, et al).
Obviously what historical fact is being denied by you is that Luther was married, with both parties never having been married before, and which Scripturally was a marriage.
Thus your charge against them is technically adultery, but which presupposes physical adultery takes place when one denies a vow he made to stay single (Luther himself had been released from his Augustinian vows by Johann von Staupitz, as the head of the order, but that likely did not absolve him of his vow of chastity according to Rome).
(Also, contrary to the charge or inference that he left Rome in order to have sex are his writings prior to that in which he said at that time that he had no intent to marry, and which only occurred some years after his excommunication.)
Thus what we deny is that Luther and Kathrina were necessarily bound by the vows they made at that time. In Scripture vows that God confirms must be kept (but not a "Herod's vow"), yet religious vows made as an unbeliever are not necessarily binding, and as we see it both Luther and wife were no more born again when they made their vows than a Muslim is.
And as in Scripture lifelong vows of clerical celibacy are not required, and even if one marries after making a vow of celibacy then they are married, then the charge of fornication does not apply.
That they were living in adultery rests upon the premise that Rome has the power to bind such to celibacy, which premise is what we deny, and thus is the real issue.
I am typing this on a laptop which for me is even slower than normal, so i am being somewhat brief.