Martin Luther made vows of celibacy within a human organization which had declared him eternally dead. Death has always been seen as freeing one from such vows.
More importantly, his Augustinian prior, von Staupitz, had formally released him from his monastic vows...within Staupitz's power, even assuming the legitimacy of the Roman Church.
This was at a time when Cardinals and Popes routinely had multiple concubines...
Luther was a faithful husband and pastor...a model for chaste behaviour, which even his worst enemies couldn't condemn.