He said the woman gave him a phone and the pair would text and she would call.
Some of the messages were about sex, what the boy called "sex messages".
"Like, she'd talk about her boob and stuff... Yeah, I don't really like talking about it, eh?"
One from the woman declared: "I love you".
The pair also sent each other pictures.
"She was sending photos and I was sending photos as well. Like, she was sending photos of her body parts.
"And I'd send photos of my body parts and stuff."
The pictures included snaps of the woman's breasts.
At one point the woman messaged the boy, saying: "Answer your phone or I'm gonna post these up."
She was referring to pictures of the boy's "private parts", he said, and she was angry he wasn't replying to her texts or answering her calls because he was busy.
On other occasions the woman would text another man she was seeing and the messages would come to the boy as well.
The boy said the man knew the woman was texting someone else.
"Yeah [he] knew, but he didn't know how old I was."
The boy didn't tell anyone about what was going on, saying the woman told her not to.
The texting stopped last year.
"Don't tell them the truth," the boy said he was told.
The boy said that in 2013 he and the woman went to a hotel at Paraparaumu and he got her pregnant.
She told him a couple of weeks later, he said.
"But then she didn't end up having a baby. Oh, she said she went to hospital and they ... Oh I don't know what that was called but they, I don't know, they killed the baby or something."
At one point the pair were having disagreements over text after the boy suffered a family bereavement.
"Stuff you and your stupid baby," the woman texted.
And there was another tense exchange.
"Some f'n boyfriend and father you are," the woman texted when she was angry.
"We are over. You can have your baby or your family can cos, F that, I'm not going to."
The trial continues.
