Basil McCrea, the leader of the NI21 party, has told the Belfast Telegraph that he is to leave politics.
Mr McCrea, an MLA for Lagan Valley, told the newspaper he would not contest the assembly election and was seeking a new career in business or public life.
He said he had become disillusioned with the political process.
NI21 was set up by Mr McCrea and South Down MLA John McCallister, after they quit the Ulster Unionist Party in 2013.
However, the party imploded on the eve of a European election in May 2014 when Mr McCrea fell out with deputy leader Mr McCallister over whether the party should define itself as unionist.
Earlier this month, the assembly standards commissioner dismissed all complaints of misconduct brought against Mr McCrea.
A report cleared Mr McCrea of claims of inappropriate behaviour and sexual misconduct towards his staff.
However, standards committee MLAs said the manner in which he occasionally treated his staff fell short of the standard they would encourage.
Mr McCrea claimed the allegations were a conspiracy to force him to resign.
Speaking to the Belfast Telegraph, Mr McCrea said: "Over the past 10 days or so a number of family members were upset by the reality of politics in Northern Ireland.
"Personally, I can take the rough with the smooth, but no man is an island and you have to take on board what family and friends are feeling."
He added: "There's no doubt the pressure over the past two years was constant and at times severe.
"It did have an effect on my health, my relationships and my general wellbeing."
'Degree of charisma'
BBC Northern Ireland political editor Mark Devenport said while Mr McCrea had polled well in the last assembly election, it was by no means certain what would have happened this year.
"There's no doubt that he was one of the better speakers in the chamber and is a man with a degree of charisma," he said.
So it may will be that he'll find another niche.
"But at the same time, on the CV, anybody who enquires into NI 21 will see that it wasn't the kind of great hope that it was meant to be to start with and it's been quite a dramatic tale of a fall from grace."