Image copyright AP Image caption Justin Harris (L) and Leanna Taylor

The ex-wife of a Georgia man who is on trial charged with murder in their toddler son's hot car death has testified he "destroyed" her life.

Leanna Taylor said she was "humiliated" by Justin Harris' serial infidelity, but told a jury he loved their son, Cooper, and did not mean to kill him.

The court heard Mr Harris sexted a teenage girl from work as his son was dying in the overheating car outside.

Ms Taylor was appearing as a defence witness for her ex-husband.

Lead prosecutor Chuck Boring suggested that Ms Taylor did not know her husband as well as she thought.

The children left behind in hot cars

He asked if she knew Mr Harris, whom she divorced earlier this year, was using Craigslist to arrange sexual trysts with both men and women.

Image copyright AP Image caption Leanna Taylor cries as defence attorney Maddox Kilgore shows the jury a picture of her son Cooper

She testified she had caught him sending text messages to other women, but did not realise he had a sexual relationship with any of them.

"If I had, I would have divorced him then," she said.

The prosecutor reminded Ms Taylor that barely three weeks before their son died in June 2014, Harris had met a prostitute for sex, while telling her he was helping a friend move.

Ms Taylor acknowledged she did not realise the extent of Mr Harris' double life.

"He destroyed my life," she said, looking at her ex-husband. "I'm humiliated. I may never trust anyone again because of the things he did.

"If I never see him again after this day, that would be fine."

Image copyright Facebook Image caption Justin Ross Harris and his son, Cooper

She became tearful during her testimony and the judge ordered the court to take an early break.

Ms Taylor earlier told jurors that her sex life with Mr Harris had problems, but he was a good parent to 22-month-old Cooper.

"He wanted to be the one to push him on a swing," Ms Taylor said.

"He wanted to be the one to slide down the slide with him. He wanted to enjoy every second he could with him."

Defence attorney Maddox Kilgore asked her: "Did Ross love his little boy?"

"Yes, he did," she replied. "Very much."

Mr Harris, who avoided eye contact with his wife, cried at times during her testimony.

On the day of Cooper's death, he was supposed to drop the boy off at daycare but instead drove to Home Depot where he was employed as a web developer.

Mr Harris says he forgot that he had left his son strapped in his seat in the back of the car, where he was discovered later that day.

Previous hearings heard that outside temperatures on the day of Cooper's death in June 2014 reached almost 90F (32C).

Mr Harris, who has pleaded not guilty, faces a maximum sentence of life in prison.