The Victorian Greens leader, Ellen Sandell, says former co-deputy leader Sam Hibbins will never be welcomed back to the party room after he admitted to a relationship with a staffer that broke the party’s rules.

Sandell said Hibbins resigned from the party room this week after MPs suspended him. She said she also requested his resignation as a Greens member, which he provided.

Hibbins, the member for Prahran, announced on Friday morning he would quit the state party room after saying he had a “consensual relationship” with a staff member in his office.

The Prahran MP released a statement saying the relationship ended “some time ago” but it was a breach of the party’s rules. He will sit as an independent MP.

Sandell said that neither she, nor any Greens MPs or supervising senior staff, had any knowledge of the relationship before it was brought to her attention this week.

“The Member for Prahran has completely lost my trust, and the trust of his colleagues, and he will never be welcomed back to our party room,” Sandell said.

Hibbins, who is married with two children, said the relationship was “a significant error of judgment” and he understood “the distress this has caused”.

“I accept the consequences of my decisions that affect my personal and professional lives. I am working to make amends to the most important people in my life, my family and our community,” he said.

“I’ve always worked hard to advance the Greens’ cause, and know this is a distraction from my work and the work of the Greens, but I remain committed to serving my electorate of Prahran.”

In a video posted to Instagram, Hibbins said the relationship was “short”.

“I deeply regret what’s happened. I’ve made a very human mistake but I am working to find the best way forward,” he said.

In his statement, Hibbins, said he understood this incident would “shake people’s trust in politicians” at a time when “people are struggling and are already disengaged from politics”.

“We are human, and we make mistakes,” he said.

“The important thing is making amends and focusing on what really matters. For me, it’s my beautiful family.”

Hibbins said he would continue to fight for “the fantastic community I love and live in, Prahran”.

Hibbins has been the MP for Prahran since 2014. He holds the seat on a 12% margin, on a two-party preferred basis.