In politics, as in marriage, any decision to walk away from the relationship often turns out to be easier than what follows.
When John McCallister and Basil McCrea left the UUP, they were also, in a sense, leaving the family home. They leave behind friends and members who have knocked doors and canvassed for them.
It's never an easy decision to leave a political party. And it's never easy knowing what to do next. Well, they have decided to form a new political party, even though it will need substantial funding, membership and organisation.
They will be disappointed that David McClarty has decided to remain independent: but they will, nevertheless, be given party status in the Assembly (complete with about £50,000 of additional funding) and that will provide them with a very potent media/political platform.
But, when their new party gets off the ground, what do they call it and where do they position it? If they include 'unionist' in the title, then it's going to look like a home for disgruntled former members of the UUP.
If they don't include 'unionist', they will face accusations that they aren't really unionists at all. And if they try and pitch themselves somewhere in-between, how do they differentiate themselves from Alliance?
To some extent, the name they choose must reflect the voters they are targeting and the policies/agenda they want to champion.
It isn't enough to go on about a liberal/secular/pragmatic/moderate demograph that has given up on carve-up politics and wants something new.
Those people don't vote Alliance, nor have they been attracted by the Conservatives, Greens, or Ukip. So what's the unique selling-point of a new party? What would McCrea and McCallister offer that hasn't already been offered?
Put that another way: unless you have a pretty good idea why so many voters within the pro-Union community have stopped voting – or never acquired the habit in the first place – how do you know what to offer them?
Voters switched from UUP to DUP and from SDLP to Sinn Fein, because they saw two parties which were doing much the same thing as the other two parties – but doing it an awful lot better.
So how does an entirely new party convince opted-out and non-voters that it can make a real difference to politics here?
They are going to have to build a political/campaigning structure from scratch. That's going to require volunteers, commitment and hard cash.
They will need a policy bank, a media strategy, a presence in every constituency and an array of new voices to act as spokesmen.
Both men have had a very high profile over the last year, but that's probably because they provided good copy as internal critics of Mike Nesbitt and the direction he was taking the UUP.
But unless they come up with something interesting and challenging, they may find the attention of the media will wander elsewhere.
That said, a brand new, soft-u, small-u, pro-Union party has a number of things in its favour. There is political stability and an Assembly: and that gives them something to aim at.
If their pitch embraces 'opposition,' alternatives and choices, then they have a strong case to make in terms of getting 'new' voices and a 'new' party into the Assembly.
Nesbitt's lurch towards the DUP has left unoccupied territory for a new party to claim; territory which Alliance has never been able to claim and which the Conservatives and Ukip don't even recognise.
Indeed, a new party may pick up votes from Conservatives, who have given up on making their own breakthrough.
Most important of all, though, is the enormous pool of non-voters which now exists across Northern Ireland. If a new party (particularly one which starts with a base in the Assembly) can find a way of tapping into key sections of that pool, then it has a very good chance of adding to its numbers at the next election.
Forming a new party, anywhere, is never easy, but there is clearly space for the sort of vehicle Mc Crea and McCallister have been talking about.
They will face challenges from mainstream unionism and Alliance.
Yet, if they attract support, volunteers and donations, they are well-placed to change the political landscape. But – and it's a big but – they need something more substantial than the contents of their first 'announcement' document last week.