When he saw his girlfriend dancing with a male stranger at a night club, he got upset and scolded her.
Later that night in bed, Mr Lee Yang Boo, 55, accused Sukanya Praphuttha of having a sexual relationship with the man and hurled vulgarities at her. In a fit of anger, she attacked him and stomped on his head so hard that she fractured his skull. He died a few hours later.
At 156cm tall and weighing 55kg, she was 10cm shorter than Mr Lee but 10kg heavier.
Yesterday, the Thai national, who is a Singapore permanent resident, pleaded guilty to killing Mr Lee and was sentenced to 5-1/2 years in jail for culpable homicide.
Some time during the assault in their North Bridge Road flat in the early hours of March 1, 2015, a neighbour heard Mr Lee shouting "Don't beat me" and "Stop beating me", the court was told.
Praphuttha, 43, and Mr Lee had lived together in the rented flat for seven years. They had a tumultuous relationship, marked often by quarrels and, at times, physical fights.
On the night of Feb 28, 2015, after going for drinks with friends at a nightclub, where she danced with a stranger, they returned home.
After more drinks, they quarrelled after Mr Lee made the sex accusation. But she eventually placated him and they went to bed.
Later, Mr Lee suddenly woke up and continued to hurl vulgarities at Praphuttha and insulted her parents as well.
A scuffle ensued, which resulted in Mr Lee lying down on his side on the floor of the bedroom.
With her right foot, Praphuttha stomped on the left side of his head. She claimed that she lost her temper when he continued to hurl vulgarities, so she hit him repeatedly on his face, body and limbs.
As she helped Mr Lee onto the bed, she noticed that his left ear was bleeding and he was having breathing difficulties. At about 4.30am, she sought help from a neighbour, who called the police.
Mr Lee was pronounced dead in hospital at about 6.45am.
An autopsy concluded that he died from head injuries "most likely caused by heavy blunt force impact to the sides of the head" and "most likely inflicted by a broad surface". A total of 47 bruises were found all over his body.
Praphuttha was found to have a handful of bruises and abrasions.
She was initially charged with murder but the charge was reduced to culpable homicide, which carries a maximum of 10 years in jail.
Deputy Public Prosecutor Mohamed Faizal sought a six-year jail sentence, arguing that Praphuttha had viciously attacked Mr Lee when he was already "down for the count". Mr Lee died a slow and painful death, he said.
Praphuttha's assigned lawyer Cheryl Ng argued that his "highly provocative" insults at her parents triggered her reaction. She asked for four years in jail, saying her client regrets killing the man she loved.
Ms Ng said Praphuttha moved here in 1991 when she married a Chinese national, with whom she had a daughter. After they divorced, Praphuttha got to know Mr Lee and later moved in with him.
Mr Lee's sister, who was in court, said her brother suffered a death he did not deserve.