Stormont, the seat of Northern Ireland's devolved legislative power, did not follow England, Wales and Scotland after the British parliament in Westminster voted by a huge majority to legalize same-sex marriage in 2013.
Following the Westminster vote, Stormont held five votes before a slim majority returned a vote in favor of legalization in 2015.
However, this was immediately contested by the Democratic Unionist Party, which tabled a "petition of concern" -- a mechanism that can be used by lawmakers in Stormont to flag up motions before the assembly that could fall across sectarian lines, and so must have both cross-party and cross-community support.
Because of Northern Ireland's unique status and history, Stormont operates on a power-sharing agreement, requiring parties representing both republicans and unionists communities to govern together.
That agreement fell apart in 2017 and has only recently got back on track. During that time, Northern Ireland effectively had no government, which meant politicians in Westminster had to ensure that the province still functioned, despite Stormont not sitting.
On October 7, 2019, Westminster passed legislation that would legalize same-sex marriage and abortion on January 13, 2020, if Stormont was not back up and running by October.
Despite the recent return of power-sharing at Stormont, that deadline was missed.
Prime Minister Boris Johnson is visiting Northern Ireland on Monday to meet leaders representing both unionist and republican communities, but given how strong opposition to same-sex marriage has been in Northern Ireland historically, it's highly unlikely he will discuss the issue.
CNN contacted Downing Street to ask if Johnson would be raising the matter, however, at the time of publication, there had been no response.
The Republic of Ireland legalized same-sex mariage in 2015