Has Nortern Ireland ever held an election for seperation from the British?

What were the results. Because from what I understand, the British are under the stance that N.Ireland will remain British until a majority vote declares that N.Ireland would want to be free.

no, there has never been a referendum to decide this. If anything, the majority has been protestant,so it would be unlikely there would be a call for such a vote.
They have their own national parliament now, so maybe in another 50 years, they might have one. But by then , who knows there could be a federal Europe, so it would make no odds.
Scotland at the moment are hinting at full separation from London rule. They have their own parliament too, but I think a majority of Scots don't want that either, and I imagine these feelings are echoed in N Ireland

Strictly speaking, the answer is YES.

After the 1922 settlement, there was a vote held in every part of Ireland to decide whether to remain under British rule or to throw thier lot in with the newly created Irish Free State.

It was the outcome of those votes that determined the modern-day borders of Northern Ireland.

The people of Northern Ireland are free.
They have decided that they wish to remain British until the majority wish not to. This is Democracy. It is the IRA who want to get rid of the British by Non democratic means

There was a referendum held sometime in the 1980's in which the majority chose to remain "British" (I remember voting)