But Rimoni Muliaga claims he did not intend to murder his wife and asked a jury to find him guilty of manslaughter.
The 44-year-old faced his first day on trial accused of murdering his wife Lise Muliaga, 37, in September 2023.
The couple had relocated with five children from their home in New Zealand to Melbourne in July of that year and initially moved in with Muliaga's sister at St Albans.
They moved into a bungalow at the back of Muliaga's brother's Melton South home about a week before the killing.
After moving in, Muliaga argued with his wife about his belief she was having an affair with his brother.
On September 18, following one such argument, Mrs Muliaga went for a walk on her own and when she returned her husband had armed himself with a kitchen knife.
Muliaga stabbed his wife four times in the upper body inside the backyard, including to her chest, and she bled to death.
A jury was empanelled in Melbourne's Supreme Court on Wednesday, after Muliaga pleaded not guilty as his lawyers claim he did not intend to commit murder.
Prosecutor Patrick Bourke SC said some of Muliaga's family, including his brother and sister-in-law, will give evidence about the lead-up to, and day of, the killing.
This includes arguments they overheard between the couple where Muliaga accused his wife of sleeping with his brother and claims he had assaulted her twice before the killing.
On one of these occasions Muliaga allegedly pressed his wife "up against the wall with his hand against her neck", Mr Bourke told the jury.
"It's clear he was angry at his wife because he believed she was being unfaithful to him with his brother, that was his belief at the time he stabbed her," he said.
"That motive, that reason, we say might help you in your task of deciding what his intention was when he went about stabbing his wife four times."
Muliaga's barrister Michael McGrath said his client, who had an intellectual disability, admitted he killed his wife but did not do so with the intent to murder her.
He said Muliaga's disability and depressive disorder had impacted his reasoning and ability to self-regulate.
"This is certainly a tragic case where a woman has been killed by her husband, and there's no dispute about that," he said.
"The issue in this case is being able to distinguish between the result of his actions - the death of his wife - and his intention at the time, they're two very different things."
He said Muliaga's intent was the "central issue" in the case and if murderous intent could not be proven beyond a reasonable doubt then another charge was open to the jury.
"The charge of manslaughter is the correct charge in this case, and you could find him guilty of manslaughter not of murder," Mr McGrath said.
The trial continues.
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