In 1949, the Irish Free State became an independent republic (the Republic of Ireland) & formally left the Commonwealth. Since then, it has moved slowly from an inward-looking, church-dominated, impoverished state to an outward looking, open, prosperous, democracy, and it has integrated further into the EU. On the other hand, Northern Ireland has remained a territory within the UK with little representation and almost no political power.
From 1960s, despite some temporary ups & downs, relations between the Republic of Ireland & the UK have become better and better. However, complete reconciliation between them will not be possible until a political solution to the problem of the Northern Ireland is found.