"I've offered to pay for her bills. It wasn't for her to spend when she was in trouble.
"She might not have had money at the time, it's not easy to live on the dole or whatever.
"It's all for my kids, mate. At the end of the day, it's all for the kids," Mr Graham said.
A joint account the pair had together had been set up for their twins' 21st birthday party, Mr Graham said.
They had not been a couple in almost 20 years and only had a "friendly relationship", he said.
When he had been seen at Reiri's house by the landlord, it was because he had gone to the house after work to look after his youngest son when Reiri was not home, he said.
"I just try to keep a good relationship with my kids.
"That's pretty much what I go around there for."
He said that, during the period in question, he had never lived with Reiri and usually returned to his own home after visiting the children, although he sometimes slept on the couch when Reiri was away.
When asked by prosecution lawyer Anitesh Govind why he had provided Reiri as his next of kin contact on several forms, Mr Graham said after his mum died he had put Reiri as next of kin as she was the mother of his children.
When Mr Govind pointed out the 18 rent payments he had made for Reiri's house from 2012-14, Mr Graham said he might have paid the rent if she did not have the money at the time or had been out of town for work.
When questioned by Mr Govind, Mr Graham denied supporting Reiri.
"I'm helping her pay for whatever for the kids, mate.
"I'm a Maori and that's what we do, help each other."
Earlier, the court heard a recording of Reiri being interviewed by ministry investigator Mark Schultz in 2014.
In it, Reiri denied being in a relationship with Mr Graham and said she was unsure why Mr Graham might have listed her as next of kin. "He has not been living with us and we are not in a relationship, and he's actually got another girlfriend.
"All these written statements, they must have lived in our house for them to know we were in a relationship," Reiri said.
The prosecution provided a DHB admission form that showed Reiri had listed Mr Graham as her partner, which was submitted as evidence.
In his closing statement, defence lawyer Ian Hard said a continuing emotional commitment between the pair had not been proven.
"There wasn't the emotional commitment to Keriana Reiri.
"What there was, was a commitment to make sure that the power bill was paid if she couldn't.
"Certainly things were done on occasion when she couldn't.
"All of the things he did arose from a blood relationship with his own children."
Judge Bill Hastings reserved his decision until September.
Reiri was remanded at large.