As a child, I became aware that one of the oddities of my Dublin home was that my Roman Catholic parents had Protestant friends.
Not only that, but at a time when the catechism I learned at school encouraged sectarianism, my father, Professor of Modern Irish History in University College Dublin, set up cross-border history bodies to help challenge the narrow nationalist view of Irish history.
So, by the time I left Ireland in 1965, I had attended students' history conferences in Magee College and Queen's, as well as in Trinity College Dublin, a university the Archbishop of Dublin warned Catholics was off-limits. I knew a few unionists slightly.
I used sometimes visit Northern Ireland in the terrible days of the early 1970s to see my close friend, Liam Hourican, RTE's correspondent, and in our conversations there and in London I learned a great deal from him, for Liam had imagination, empathy and friends across the sectarian divide and burned to explain unionism to the rest of the island.
He was angry with the prevailing nationalist view of unionists, which he described in a brilliant television talk in 1974.
The spectrum of nationalist attitudes, he said, spread from "the view that the northern Protestants are a lost tribe, which will one day return to us to the much more hostile, but not unrelated, belief that they are an incorrigible colonial remnant who may conform, or get out".
Such attitudes, he added, had established "a climate of tolerance for Provisional violence; I would also argue that they have supplied the Provisionals with their internal self-justification".
Liam left journalism and died in 1993, by which time – from attending Anglo-Irish conferences – I had already acquired some unionist friends and discovered something of the ignorance and bigotry so many nationalists displayed towards them.
During the last couple of decades, since I began reporting on Northern Ireland, I learned how right Liam had been. I blame some of the animosity on our tribal inferiority complex.
We couldn't bear the thought that those we thought were on top didn't like us and we hated them for it. We called them bigots (I still laugh about how furious nationalists used to be when unionists mentioned Rome rule), but were ourselves unprepared to make any effort to get to know them and understand them.
There was nothing new about that. The leaders of 19th and early-20th century constitutional nationalism couldn't be bothered, either. And the 26 counties laid claim to the six and otherwise wanted nothing to do with Northern Ireland.
I always believed that, if there was a genuine desire for a united Ireland, the route should have been seduction, rather than intimidation, but though the nationalist tribe is famous for its articulacy and charm, it expended none of those talents on unionists.
I hope my unionist friends will forgive me when I say that I came to view their community as a bride so desperate to avoid a forced marriage that she would do anything to save herself from being dragged to the bedroom, which is why I became a trenchant critic of the violent would-be bridegroom.
It was violence that copper-fastened partition and we should never let the perpetrators forget it.
When I became close to unionists and even to many good people in the loyal institutions, I was taken aback by the hostility I received from nationalists, who viewed me as a traitor.
I remember a ridiculous argument in Dublin in the late 1990s, when intelligent, well-educated people shouted at me that, if David Trimble really wanted peace, he would instruct the Orange Order to abandon Drumcree.
Attempts to explain that unionism – and particularly Orangeism – were not governable in the way a Catholic culture imagined were angrily shouted down.
Well, the bride stayed chaste and the bridegroom learned some manners. Indeed, the southern Irish discovered they didn't fancy a marriage after all, but would prefer a distant platonic friendship.
However it works out, it's a great leap forward that north and south are now treating each other with some respect.
Liam Hourican would be pleased.