Brexit (You might begin to understand now why the EU and Ireland will never submit to Boris's tough guy act and why his "negotiations" are all just a vain show. It's not intransigence on their part, it's bringing Britain to heel on its irresponsible demands. And that will not change.
So, British leavers can huff and puff about a hard Brexit all they want, but they won't get a deal that drags Northern Ireland away from its integrated relationship with the South; and with no-deal off the table, their only other option will be to draw up a customs border between themselves and Northern Ireland. In other words, initiate a de facto break-up of the UK—which would just be the beginning as Scotland would almost certainly desert next with Northern Ireland very possibly then going the whole hog and joining the South).