Mark James Bombara, 63, shot dead Jennifer Petelczyc, 59, and her daughter, 18-year-old Gretl, at their Perth home on May 24, 2024, before killing himself.
An inquest is examining the circumstances of their deaths.
Several witnesses had described Bombara as "fixated" on his failed marriage, counsel assisting the coroner Rachael Young said in her opening remarks.
Bombara's mate of more than 20 years, Allan Maher, says Bombara was acting erratically and "would not shut up" about his estranged wife, Rowena, before the killings.
"He couldn't get his head around the fact that she had left him and he couldn't understand why," Mr Maher told the WA Coroner's Court.
The Bombaras separated in April after 35 years together.
"He was a short, fat bloke, and he had a trophy wife, tall, blonde, long-legged, good-looking," Mr Maher said.
"He couldn't cope with the fact he'd lost the trophy."
Mr Maher said Bombara viewed being married to her as a "victory".
"It was all about pride; he couldn't accept that he'd lost the thing that was possibly the most valuable thing he had," he said.
Bombara believed he had done nothing wrong and was focused on ensuring Rowena did not get access to their money, Mr Maher said.
He recounted Bombara saying: "I'll get the bitch ... I'll get that c***".
"He was rambling," he said.
Mr Maher said Bombara blamed his daughter Ariel for his marriage breakdown.
"Ariel and Rowena were rolled into one unit, and he said he didn't get on with Ariel," he said.
"They were working together to get him."
The inquest has heard the Bombara's marriage break-up was bitter and Rowena had been the victim of coercive control and verbal and physical abuse.
Jennifer and Rowena had been friends for years, and Jennifer had helped her friend during the split.
Ariel's lawyer Kathryn Kraus said that after Rowena left Bombara, she and Ariel went into hiding "in fear for their lives".
"Rowena was fearful that Mr Bombara would kill or injure her," she said.
Rowena and Ariel reported their concerns to police on multiple occasions.
Officers noted that Bombara had access to multiple firearms and was a jealous and controlling man, but the issue was not sufficiently escalated, Ms Kraus said.
"The WA Police Force had sufficient information to issue a police order and to seize Mr Bombara's firearms," she said.
"Despite this, neither of those actions occurred."
The inquest is examining the police response to eight triple-zero calls before the murders and the family violence allegations against Bombara.
It will also investigate whether he should have been licensed to hold the 13 firearms he owned.
Bombara's medical care after he had several strokes and started experiencing mental instability will also be investigated.
The inquest earlier heard Bombara was angrier, moody and at times "unhinged" after his strokes.
The inquest continues on Tuesday.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
Men's Referral Service 1300 766 491
beyondblue 1300 22 4636
13°C