Irish woman Cathrina "Tina" Cahill, who killed her fiancé in Sydney in 2017, allegedly stabbed him in the head two years before the murder.

The Irish Independent reports that a former housemate has testified she saw Cahill walk up the stairs with her hand behind her back, then suddenly stab David Walsh in the back of his head after the couple argued on October 3, 2015.

Cahill, 27, gave evidence in the NSW Supreme Court on Friday at her sentence hearing for the manslaughter of Walsh, 29.

Cahill has pleaded guilty to stabbing Walsh in the neck on February 18, 2017, at the Passtow home the couple shared with two other Irish nationals.

Read More: Trial of Irishwoman accused of murdering fiance begins in Australia

During the hearing, Cahill told a judge of Walsh’s repeated violence, including punching strangers, biting her, and accusing her of sleeping with other men.

When her barrister James Trevallion asked how she felt about what she had done to her fiancé, she said: "There is not a day that goes by when I don't think about David's family.”

"I loved him so much.

Tina Cahill and David Walsh.

Tina Cahill and David Walsh.

"He told me no matter what I did I would never get away from him and if I ever got with anybody else he would make my life hell."

She said Walsh blocked people from her social media accounts, deleted texts and numbers from her phone, and punched holes in the house walls.

Cahill said he would grab her face "and constantly bite me, that was his thing.”

She denied a suggestion from prosecutor Nanette Williams that she wanted to minimize the violence she had done to Walsh and maximize what he had done to her when describing their relationship.

Read More: Wexford man murdered in Sydney was on the run from the police

In response to the former housemate’s testimony that Cahill had stabbed Walsh in the back of the head after an argument in 2015, Cahill said that Walsh blocked her at their bedroom door with a knife in his hand and as she went to grab it, cut her hand and then cut the back of his head.

Williams suggested Cahill was lying because she knew the housemate's evidence was very "damning" about her going downstairs to get the knife and attack her partner in the head.

"That isn't true," Cahill replied.

The Irish Independent reports that the hearing will continue on November 9 before Justice Peter Johnson, who said he expected to sentence Cahill before December 14.

Tina Cahill and David Walsh.