"I loved him very dearly." Sydney woman who killed her fiancé speaks in court.

An Irish woman who killed her fiancé in Sydney has told a judge she did not leave the “controlling and fairly unpleasant” man as she loved him dearly.

“I honestly thought he was going to change,” Cathrina “Tina” Cahill said on Tuesday at her sentence hearing in the NSW Supreme Court.

“He was someone I did love and adore.”

The 27-year-old has pleaded guilty to the manslaughter of David Walsh, 29, who she stabbed once in the neck in the early hours of February 18, 2017, at the Padstow home they shared with two other Irish nationals.

Her plea was based on substantial impairment due to an abnormality of the mind.

At the time, she was on a good behaviour bond and the subject of an Apprehended Violence Order issued to protect Mr Walsh, after she was convicted of recklessly wounding him with a glass candle holder in 2015.

Cahill previously gave evidence about his repeated violence, including punching strangers and biting her all over her body, his accusations of her sleeping with other men and his deleting texts from her phone.

Prosecutor Nanette Williams on Tuesday noted Cahill told police, after an AVO was issued against Mr Walsh to protect her, that she held no fears against him.

“I was in fear of getting in more trouble from David if I told the truth,” she said, saying she also wanted to protect him.

She had packed her bags many times to leave him, but Mr Walsh would tell her everything was going to be different.

“He would be making me dinner, buying me flowers, buying me a teddy bear but after two to three weeks it would go back to the way it was.”

She agreed with Justice Peter Johnson that her evidence revealed a “pretty stormy relationship” and that Mr Walsh might be seen to be a “controlling and fairly unpleasant person”.

But she said she stayed with him as “I loved him very dearly”.

The fatal attack occurred when an intoxicated Mr Walsh launched an unprovoked attack on a man invited into the home by Cahill and the two other female housemates.

Cahill, who also had been drinking, was punched by her fiancé when trying to stop the attack, before she took out a “large, very sharp, bladed knife” from the cutlery drawer and stabbed him.

Ms Williams submitted it was “an attack of extreme violence” upon a relatively young man who was being actively restrained by a third person at the time.

The cases of violence from Mr Walsh to Cahill, on the agreed facts, were limited while her attacks on him had involved a candle and a knife in an incident prior to the fatal attack.

Cahill’s barrister James Trevallion said there was no evidence his client had ever struck Mr Walsh without any provocation and noted she was smaller than him.

He submitted she had no intention to kill, the stabbing had involved a single jab and Mr Walsh was the one who initiated the violence.

Justice Johnson, who said the case involved “unusual features” such as a “type of two-way domestic violence”, will sentence Cahill on December 12.

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