Ireland stopped being an independent nation back in 1972 when they joined the European Union, back then called the European Economic Community. They have been a province of that empire (as José Manuel Barroso called it) ever since, and their national character was chipped away and eroded with increasing intensity directly proportional to the extent of that empire’s power over its “member states” (read: client states).
The EU’s abuse of power was one of the reasons for “Brexit”, of course; the EU thereupon has been engaged in continuous violation of the Good Friday Agreement due to the issue with Northern Ireland.
In the particular case of Ireland, the E.U. afforded them “cover” for Union with Great Britain (an obvious necessity) without having to have The Union.
Now, Brexit has set in motion an unpredictable chain of events, we can’t see the outcome but some sort of new structure to the relationship is inevitable.