The father of two young children allegedly suffocated by their mother has told a court at her murder trial she was controlling and manipulative.
The bodies of Harry and Elise Donnison, aged three and two, were found in holdalls in the boot of a car in Heathfield, East Sussex, last January.
Fiona Donnison, 45, formerly of Lightwater, Surrey, denies two counts of murder at Lewes Crown Court.
Paul Donnison, 48, was giving evidence on the third day of her trial.
He said he thought Ms Donnison, a former City worker, had been "playing a game" in the run-up to their deaths.
"As long as she had control of the children, she had control of me," he said.
The pair, who met in 1999, were never married but Ms Donnison changed her name by deed poll without telling him.
Mr Donnison told jurors how he was left in "complete disbelief" when he had returned home from work to find she had moved out without warning, taking the children with her.
He said he lived a "nightmare" during the months that followed.
At first Ms Donnison would not tell him where Harry and Elise were, and only ever let him see them on her terms, he told the court.
"If I did what I was told things were fine," he said. "If I didn't I was told I wouldn't see the children, and so on and so forth."
Mr Donnison admitted he had started a relationship with an old schoolfriend but said the friendship was strictly platonic until he knew his relationship with the defendant was over.
"She was controlling things and I had reached the point where you can't keep being manipulated and moved around and told what to do," he said.
"I felt like Fiona was playing a game with me. If I didn't do what she said or if she didn't have control of me, the children were the key."
Despite their issues, he described Ms Donnison as a "good mother" and said they lived in a "happy" house along with her two sons from her first marriage, now aged 15 and 18.
He said: "She would be very nice, very pleasant.
"The next day it would be something completely different - provocative, antagonistic, confrontational - it varied."
The trial continues.