There were two types of divorce during this period, neither of which really encompass the modern definition of divorce, and both of which were very rare.

There was a mensa et thoro: this meant that the pair was legally able to live separately, though they were still technically married. Neither of them could legally marry anyone else. This tended to come about if one partner was gone for long periods of time (example: if the husband were a merchant who would be at sea for months) so that the wife had the legal protection of having a husband who wasn’t present, or if one of the partners had done something that a court would define as “undeniably cruel”.

There was also marital annulment. This one is a little odder. The couple would petition the higher authority and claim that the marriage was invalid from the start. Examples for annulment grounds included lack of consummation primarily, but the grounds were a little different depending on where you were living. The church&government would examine the marriage along with the grounds presented for an annulment, and either approve or deny it. If it was approved, then it made the marriage void, and legally, the marriage was treated as though it never happened. Both parties were free to marry if they so chose.