Anthony Eriksen's Supreme Court trial began on Tuesday after he pleaded not guilty to murdering Ms Fenwick in their Sydney apartment in April 2023.
The jury was told arriving police and paramedics found Eriksen in the unit's hallway wearing a bathrobe, with dried up blood on his face, wrist and right foot.
Ms Fenwick was seen lying in her own blood.
She had been repeatedly stabbed in her heart and lungs, crown prosecutor Daniel Boyle said.
"He did it to her deliberately and did it with an intent to kill her," he said in his opening address.
The alleged weapon, a kitchen knife, was found in the sink with "slightly watery" blood dripping from the blade, Mr Boyle said.
The couple allegedly got into an argument after Ms Fenwick sent Eriksen a text message about 3.30pm with a link to house-sharing website flatmates.com.au
The message read "not sure they'd want a 60-year-old man though!" the jury was told.
Ms Fenwick was insistent that Eriksen needed to move out after financially supporting him for several years while he was unemployed, Mr Boyle said.
Eriksen allegedly told police at the scene of the fatal incident that he had consumed a "couple of drinks" of red wine during the afternoon.
"Living life is so stressful ... she just criticises me all the time," he allegedly told police.
"I don't know - it just happened."
Eriksen, who is self-represented, chose not to provide an opening statement, which Justice Andrew Coleman said should not prejudice the jury's view of the accused murderer.
The judge also cautioned jury members to be objective in their assessment of the facts laid out before them.
"You might also see he is wearing his green clothes, don't draw any adverse inference ... (or) speculate as to why," Justice Coleman said.
"It's really irrelevant.
"Don't go home and start googling ... facts about the case."
Ms Fenwick had earlier expressed grave fears for her safety, confiding to two close friends.
"I don't feel safe with him," she texted to one friend.Â
A month later, she was dead.
The trial resumes on Wednesday.
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