By Rich McKay

ATLANTA (Reuters) - The former wife of a Georgia man accused of causing the death of his toddler son in a hot car in 2014 testified on Monday that her ex-husband struggled with infidelity and a pornography addiction but was a doting father to their child.

Defense lawyers said Leanna Taylor had every reason to hate her former spouse Justin Ross Harris, who was charged with murder after prosecutors said he left their only child, 22-month-old Cooper, to die in a locked SUV outside his workplace in suburban Atlanta.

But Taylor, who divorced Harris after his 2014 arrest, has said she believes he did not intentionally kill their son.

Harris called Cooper "my little buddy," and the boy loved his father, she said in court on Monday.

"It still doesn't feel real," Taylor said, weeping as she recounted the day the boy died.

Her testimony for the defense opened the fifth week of the trial, which is expected to last at least one more week. It was moved from the Atlanta area to Brunswick, Georgia, 300 miles (480 km) from where the incident occurred, in an effort to find an impartial jury.

The defense has said Harris forgot to take his child to daycare after a father-son breakfast at Chick-fil-A, then accidentally left the boy strapped in the backseat for seven hours outside his Marietta office on a sweltering day in June 2014.

Prosecutors have said Harris, 35, committed the crime because he wanted to be free of the responsibilities of fatherhood. During the trial, they have portrayed him as a man obsessed with having sex with prostitutes and other women and texting teenagers.

Both Taylor and Harris broke down in tears in court as the defense showed the jury dozens of photos and videos of their son, beginning with an ultrasound, and ending with images of Harris playing a guitar to his young son, both laughing.

On the day Cooper died, Taylor said, her husband's shirt was "wet with tears."

Taylor said she and her husband had struggled to keep their nine-year marriage together amid his infidelities and pornography addiction.

The prosecution began its cross examination of Taylor on Monday afternoon, delving into Harris' double life and admitted philandering.

Harris, who also faces charges of sexual exploitation of minors for text messages he is accused of sending to underage women, could be sentenced to life in prison if convicted in his son's death.

(Editing by Colleen Jenkins and James Dalgleish)