When you give it some thought what a terrible word,think of all the places that are separated,Ireland,India ,Korea and many more got a mental block can’t think of any more but let’s not break up our British Isles let’s think of ourselves as members of a United Kingdom,united we stand divided we fall
Well considering that Ireland was part of the UK, Ireland hasn't really separated the UK has separated.
Just a point to make on your otherwise lovely and well thought out post.
Nation states need to be small enough for all to feel part of the same group/common culture yet large enough to be viable: thus UK is fine, but EU just an imposition. Goodness knows how large conglomerates places, like the US, hold it together.
Separation isn't such a terrible word. Co-joined twins probably grow to appreciate it, as do those previously in a bad relationship.