A man has been jailed for six years and nine months for stabbing his former partner up to 15 times with a kitchen knife at their home in Western Australia's Mid West.

Key points: The stabbing left Amanda Gibbons with abdominal injuries and a collapsed lung

The stabbing left Amanda Gibbons with abdominal injuries and a collapsed lung Kim Prunster attacked her because she was leaving him for another man

Kim Prunster attacked her because she was leaving him for another man He admitted inflicting the wounds but said he could not remember the incident

Kim Ashley Prunster, 57, attacked mother-of-four Amanda Gibbons with the serrated knife on November 12, 2017, in the bedroom of their house in the coastal town of Dongara, 350 kilometres north of Perth.

He was found guilty of causing grievous bodily harm with intent, but was found not guilty of the most serious charge of attempted murder of his partner of 34 years.

Prunster attacked Ms Gibbons on the last morning she was to spend with her childhood sweetheart before moving out, leaving her with abdominal injuries and a collapsed lung.

Ms Gibbons testified she lost count of how many times Prunster stabbed her in the back. ( Facebook: Kim Prunster )

A jury heard he was angry at Ms Gibbons's decision to leave him for a local businessman who had been a friend of the couple.

In sentencing, Justice Stephen Hall said Ms Gibbons had been ostracised by her friends since the incident and felt anxious, although she had recovered from her physical injuries.

But he said "nothing that she did justified or excused that attack".

His eyes were 'black, vacant'

Giving evidence during the trial, Ms Gibbons told the court a fight erupted after Prunster found a phone she used to communicate with her lover under a pillow.

She slapped him across the face and he dragged her out of the bedroom.

She slept that night in her car, but then Prunster asked her to come home for the weekend to discuss their separation.

They drank beer and listened to music together on Saturday night, and Prunster said he asked Ms Gibbons for a hug but she questioned why because "it wouldn't mean anything".

Then early on Sunday morning, Ms Gibbons woke to find Prunster kneeling next to the bed, centimetres from her face, staring at her.

She said her former partner's eyes were "black, vacant, like not focused", and that she felt a blow to her chest, then her stomach.

"Then I realised he was stabbing me," Ms Gibbons told the jury.

"I heard a hiss then felt the blood pumping out.

"As I rolled away I got one in my arm. I don't know how many times he stabbed me in the back."

Ms Gibbons told the court she walked bleeding to her adult son's bedroom and a neighbour took her to the local medical centre.

She was airlifted to Perth for surgery after the attack.

Prunster claimed no memory of stabbing

Prunster admitted inflicting the wounds but said he could not remember the incident.

He said he had been sad in the days leading up to the incident, but denied he was angry.

"I don't know what happened. Her face came into focus and she was crying and saying, 'please don't hurt me anymore','' he said.

Prunster testified he remembered holding a knife and having blood on his hand.

He said Ms Gibbons asked him to call for help but he drove away from the house and instead rang the man with whom she had formed a relationship, telling him he had hurt her.

The court heard Prunster then attempted to take his own life.

Stabbing was a deliberate, willed act

His lawyer, David McKenzie, told the trial his client may have been in a "dissociative state following a psychological blow".

Forensic psychiatrist Gosia Wojnarowska told an earlier hearing it was highly likely Prunster suffered disassociation, but acknowledged people could feign symptoms and psychiatrists had to believe what they were being told.

Another psychiatrist, Adam Brett, testified Prunster's "purposeful" actions of going to the kitchen, getting a knife and returning to the bedroom to stab his partner were incompatible with being in a dissociative state.

The Supreme Court was told Prunster attempted to take his own life after the attack. ( ABC News: Briana Shepherd )

Justice Hall said he did not accept Prunster had no memory of the attack.

He said his actions were "deliberate, willed acts" of a man who was angry at his partner who wanted to leave him for another man.

Justice Hall said in sentencing, he had to take into account the number of the wounds— up to 14 of them— and the nature of them.

He said Prunster had failed to get help or assistance for his former partner.

But he said he accepted he had not planned the attack and was remorseful.

Prunster was sentenced to six years and nine months and will be eligible for parole after serving four years and nine months.