Ulster Unionist MLA Mike Nesbitt has said unionism needs to wake up over the prospect of a united Ireland.
The former UUP leader also challenged nationalist and republican leaders to tell unionists that they are wanted in a united Ireland.
His comments came during a debate at St Mary's University College as part of the West Belfast Festival.
A panel of four from a unionist background, chaired by commentator David McCann, debated whether there would be a warm house for unionists in a united Ireland.
The discussion came after comments by former DUP leader Peter Robinson who urged unionists to prepare for the possibility of a united Ireland.
While DUP leader Arlene Foster stood by Mr Robinson, DUP MP Sammy Wilson described the remarks as "dangerous".
Mr Nesbitt said unionists are not good at building relationships.
"I have heard you legitimately for many years express your desire for a new unitary state on this island, recently I have also heard people talk about protecting the rights of the unionist, British community, but what I haven't heard is, 'we want you'," he told the audience.
"For me, it's not about talking about border polls or new constitutional arrangements, it's about relationships.
"There is a lack of trust building between the parties at Stormont at the minute, and if you don't have trust, you can't do politics.
"I think for unionism, we are not very good at building relationships.
"Unionism should be engaging because you have to engage with what you are uncomfortable with.
"We also have to look at how we protect unionist and British culture and identity."
Mr Nesbitt also spoke about how he had built a relationship with former deputy First Minister Martin McGuinness on a walk around Stormont, revealing that he had once told him something that could have ended his own career.
He said Mr McGuinness had kept his confidence, and described him as a "man of political integrity".
Mr Nesbitt went on to tell a story about a frog being placed in cold water which was slowly heated up, which caused it to die, because it did not sense the change.
"The atmosphere and environment around this country, between these islands and Europe, everything has changed.
"Unionism needs to wake up, otherwise it's going to be that frog."
There was criticism for Mrs Foster over her comment earlier this year that she would leave in the event of a united Ireland.
The question was put to Mr Nesbitt, along with Professor Jim Dornan, former PUP press officer Sophie Long and former NI21 party member David Honeyford whether they would leave if there was a united Ireland.
Mr Nesbitt, Mr Dornan and Mr Honeyford said no, while Ms Long said she had already moved away for a job.
Mr Dornan slammed Mrs Foster's response as "reactionary" and said he would stay because he wanted to see what the deal looked like.
Ms Long said she felt Mrs Foster was unable to be "magnanimous", speculating that she was "still traumatised" over what happened to her as a child when the IRA shot her father.
She also described a united Ireland as "uncharted territory" for unionists and loyalists, which she said made them uncomfortable.
In response to a question over when an Irish unity poll might happen, Mr Dornan said he believed it would happen in 2022, adding it should include other options such as an independent Ulster.
He also warned against Sinn Féin leading the campaign for a united Ireland, saying instead the universities should be stepping in to broaden the debate, criticising them as having been "painfully quiet" on the subject so far.
Meanwhile, during a discussion on identity, Mr Honeyford commented that he felt there was an element of "shame" at being described as having an Ulster British identity, and said that needed to change.