The 50-year-old also lied to others about Caroline Smith having gastro in the days after her May 2025 death.
But he denied intentionally killing his 48-year-old mate, his barrister told a Victorian Supreme Court jury on Wednesday.
McLennan and Ms Smith became friends at school in Western Australia, and he joined her and her husband in Victoria in October 2023.
Ms Smith's husband was diagnosed with late-stage cancer and she had asked McLennan if he could live with them to help around their house in Hamilton in far west Victoria.
After Ms Smith's husband died in September 2024, McLennan remained at the home but his friendship with Ms Smith was volatile, crown prosecutor David Glynn SC told jurors.
They had serious fights and there was an alleged incident in December 2024 where McLennan assaulted Ms Smith, leaving her with injuries to her face.
Police were not called at that time.
They did attend the property in March 2025 after McLennan told a friend Ms Smith had "gone batshit crazy".
"He seems to have felt stuck in a situation he hated," Mr Glynn said.
Ms Smith was last captured on home CCTV entering her laundry at 9.24pm on May 11, 2025.
It's alleged McLennan attacked her sometime between 9.30pm and 10pm, strangling the 48-year-old to death.
McLennan was then captured on CCTV walking into an alfresco area and saying to himself, "I'm pretty sure you killed her".
He then went to the fridge twice to grab beers before moving Ms Smith's body into a spare room, Mr Glynn said.
McLennan remained drinking at the house for the next four days, only leaving to go and buy more beer, the prosecutor said.
He also allegedly lied about Ms Smith's health, telling her driving instructor and a friend that she was unwell with gastro.
It was only when police were called to the property for a welfare check on May 15 that officers discovered Ms Smith's dead body.
McLennan had fled and tried to harm himself but officers found him in a nearby shed.
His barrister Rosalind Avis told jurors it was not disputed that McLennan was the only other person in the house at the time of Ms Smith's death.
It was also not disputed that they had heated arguments prior to May 2025, nor that he had spent the days after her death drinking, Ms Avis said.
But the barrister argued McLennan did not intend to kill or cause really serious injury to Ms Smith.
Ms Avis urged the jury to carefully consider the nature of their friendship, the extent of Ms Smith's injuries and McLennan's actions after her death.
McLennan has pleaded not guilty to murder.
The trial before Justice Jane Dixon continues.
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