They then argued about some text messages and she asked him to pull over and let her out of the car.
Mr Tasker said she initially walked away from the car but then walked on to the road and sat down.
"We were trying to pull her up but she didn't want to move. She said 'leave me alone I don't want to be near you'."
Ms Dando joined her on the road to comfort her. Then Mr Tasker saw car lights coming around a bend.
The driver of the east-bound car saw the women and braked, but still hit both of them.
"I called out to them, but it was too late - it just smacked into them," said Mr Tasker.
He said the driver helped perform CPR on Miss Waipouri. But she died at the scene while Ms Dando drifted in and out of consciousness.
Mr Tasker said he spent yesterday in shock, and wasn't sure he could face Miss Waipouri's funeral.
"I wish I could turn back the clock," he said.
In the hours before the tragedy he and Miss Dando were at a Manukau bar before going to Miss Waipouri's family home in Pukekohe.
When they left the house, Miss Waipouri came outside to walk them to their car, and decided to come for a ride to Maraetai.
"I think she might have texted her Dad to say where she had gone."
The first person on the scene after the accident said screams of "get off the road", "get off the road" could be heard seconds before the car hit the two women.
Yvonne Puti was outside her parents' house smoking when she heard the screams.
"They were saying 'get off the road, get off the road' ... Then there was a big grinding sound."
What she and her husband found at the roadside was "indescribable".
Helen's father, Neville Dando, and wife Sue were at Middlemore Hospital yesterday.
"She has a broken femur, a smashed wrist, a broken right arm, pelvis broken but not too badly," Mr Dando said.
"She's got lots of bones broken." But she was still "better than you'd think" considering a vein to her heart had also been dislodged.
Doctors were worried Miss Dando could have a head injury.
"They woke her up for a minute and she was alert, she was able to respond and move her legs.
"It's going to be a long recovery but we're hoping it's not a head injury."
It's believed the driver of the car who hit the women was on his way home from work.
He was breath tested at the scene and no trace of alcohol was found.
Police said it was too early to say whether charges would be laid.
