Tiumala's wife, Elina, had been intercepting Hayley's suicidal text messages all day and replying with abuse. She was later sentenced to a nine-month good behaviour bond on charges of intimidation.
Tiumalu told the tribunal today that his wife and two young children would suffer if he went back to Samoa, where he would probably live with his mother.
His family was likely to stay in New Zealand because "there isn't enough room for them and I can't provide for them in the same way I provide for them here," he said.
Elina Tiumalu also gave evidence at the hearing, saying her husband's deportation could have a devastating effect on their children.
She was not sure if she could raise the funds for the family to visit him and said if they moved to Samoa she was concerned about the effects of cultural differences on herself and the children.
Tiumalu arrived from Samoa in 2005 and has New Zealand residency.
In 2009 his mother and sister came to New Zealand to visit, while his family was living in Rotorua.
However, there were problems between his wife and mother, inflamed by cultural and language barriers.
In January that year he was charged with assaulting his wife after the pair argued when he returned from work. He told the tribunal he had been angry to find Elina had not cooked dinner for his mother or taken their ill daughter to get medical care, and said his wife was also dressed inappropriately.
Tiumalu was bailed to his uncle's house. He and his wife had been apart for about six weeks when he started a relationship with Hayley, the tribunal was told.
The pair met while working at McDonald's and quickly became good friends, said Tiumalu, who was drawn to her warm, kind personality.
He told her he was separated from his wife, but did not believe his marriage was over.
About a month after leaving the company, the pair went bowling together.
Asked what he thought was going to happen when they met up, he said he believed it was for friendship, and he had thought she was 17 because of the mature way she spoke and behaved, he said.
The relationship developed into a sexual one and the court heard Tiumalu and Hayley had unprotected sex three times over four months in 2009.
He said Hayley's father told him his daughter was 15, but she said she was 17.
"At the first time we had that sexual relationship I thought she was 17 years old. She said she was old enough. I kept asking her and she said she was 17."
After realising she was 15 he broke off the relationship.
"I was 27 and now realised that she was 15. Now I feel so guilty about that."
Hayley's parents Kevin and Lesley Fenton attended today's hearing.
Tiumalu has since reconciled with his wife and the family moved from Rotorua to Auckland at the end of 2009 "for a fresh start".
He went before the Parole Board earlier this year seeking release from prison, which was denied. He is due to come up for parole again in June.
The tribunal reserved its decision.
