Jay Lupton was fed up with "junkies and drama" circulating about the Lethbridge Park house, crown prosecutor Gareth Harrison told the NSW Supreme Court jury in his opening address on Monday.
And he was enraged by Hady Jaouhara saving his girlfriend Sherie O'Neill's name alongside "beauty" in his phone, Mr Harrison said.
The 30-year-old is accused of murdering Mr Jaouhara just before midnight on Feburary 23, 2020 in the backyard of the Magellan Avenue home.
Lupton denies the stabbing took place outside and said it occurred in self-defence after he was attacked by two ice users.
Thirteen days earlier Lupton sent a message to Mr Jaouhara's friend threatening to "stab the f*** out of everyone" if they continued visiting the Western Sydney home.
"I'm sick of seeing a bunch of junkies hanging there all the time," he wrote.
The friend responded that he was "sorry my bro didn't mean any harm," and that they never used drugs when children were around.
But days later when Lupton figured Mr Jaouhara was romantically interested in Ms O'Neill, he punched him through a car window and used his keys to write DOG on the bonnet.
The jury was read more than 100 text messages between Lupton and Ms O'Neill detailing his growing bitterness and distress over their relationship status.
"I'm over you treating me like some c*** you can get when you want to," he wrote in one.
"Answer now or I'm coming to kick the door in (I don't give a f***) who is there you will regret f***ing me over," he said in another.
Less than 12 hours before the stabbing he wrote: "Tell your f***ing sister to shut her mouth or i'll take her (boyfriend's) life in front of her".
The crown case is that Lupton turned up that evening "looking for something" and found his victim outside who Ms O'Neill told to "leave, go now".
"Don't go f***ing anywhere," Lupton allegedly said before lunging towards him and stabbing a knife into his chest.
Defence barrister Angus Webb disputes this version, saying Lupton arrived unexpectedly.
"And what's happening?" Mr Webb said.
"The Ice is out."
An argument erupts between the drug users and Lupton who is assaulted before picking up a knife that was "unfortunately used" inside, Mr Webb said.
The jury will hear from a number of "untruthful" witnesses - including Ms O'Neill - all of whose recollection is tainted by their drug history, he said.
Mr Webb said the jury should keep an open mind to his client's anger that day, which was fuelled by Ms O'Neill's relationship with another ex-partner, not with Mr Jaouhara.
The trial continues.
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