This is the ignorance I was referring to. NI is one of the four component countries in the United Kingdom (read the cover of your passport), it does indeed have a flag, and "God Save the King" is the only official anthem in the UK. (Trying to choose an alternative in a society as divided as NI is impossible).
The trajectory is not necessarily towards unity.. an independent NI within the EU was also a possibility, as was an independent Scotland+NI union. We were all doing quite well before 2016, as joint membership of the EU allowed the zealots on both sides to frame cooperation between RoI and UK on Northern Ireland as "Intra-EU coordination", rather than "meddling" or "oppression". Even with NI in the UK, eventually the border would have become something minor, like the Danish/Swedish frontier, and everyone would have been fine with it, but oh no, David Cameron had to use the UK as a proxy in the petty infighting of the Tory party, and so we're back to the 1950s again...
@Finnegan Palestine is a deceptive and misleading parallel to NI, especially in the present day. It's a trope that Sinn Féin and company like to trot out, but it has always been hyperbole, and an insult to the experience of the Palestinian people, most especially in the present.