The girlfriend of a professional cage fighter accused of killing his friend has admitted sending a flurry of abusive text messages instead of calling for help.

Bradley Dusan Fletcher, 39, is standing trial for the murder of 32-year-old Bradley Evennett on March 22, 2024,  when they sparred with boxing gloves on as they celebrated moving into a sharehouse together.

Fletcher's then-girlfriend Jasmine Robinson, who was also due to move into the Melonba house in Sydney's northwest, gave evidence in a NSW Supreme Court trial on Monday.

Ms Robinson became angry with Fletcher about an ex-girlfriend he allegedly contacted after killing Mr Evennett, defence barrister James Trevallion SC told the court during a cross-examination.

Ms Robinson conceded her relationship with Fletcher had been tumultuous and that she had assumed at the time he was cheating on her.

Before presenting to police or contacting emergency services, Ms Robinson sent a series of abusive and threatening messages to the ex-girlfriend including 'This is your fault, 'You've twisted him up' and 'I'll kill you sl** deadass'.

'I was angry,' Ms Robinson told the court.

Ms Robinson said the men had spent the afternoon drinking and doing 'boy stuff' and appeared to be having fun with each other.

'They were out the back being hoons. Just mucking around like children,' Ms Robinson said.

Ms Robinson, who wasn't drinking with the men, left the house to attend to other matters but later received a call from Fletcher telling her to come back.

When she arrived back at the house, Ms Robinson said she saw blood and Mr Evennett lying face down on the grass in the backyard with Fletcher pacing up and down.

'I've said 'what the f***, what the f***'s going on here, why have you done this?'' Ms Robinson said.

'He's charged over towards me. He's like 'I had to. He doesn't care about your safety, you don't understand'.'

Fletcher allegedly went to pick Mr Evennett up which Ms Robinson said caused her to scream to put him down.

'That's when he came at me and said 'shut the f*** up, I'm going to kill you too',' she said.

Mr Evennett's body was found dumped on a footpath with a head injury, bleeding brain, broken eye and facial bones, broken teeth - including a molar found in his airways - rib fractures, and abrasions on his limbs and neck.

Fletcher pleaded not guilty to murder, claiming Mr Evennett's death occurred by accident during their sparring session.

The now 39-year-old pleaded guilty to manslaughter, however the lesser plea was rejected by prosecutors.

The trial continues.