"I'm gonna kill him the mad white dog," Robinson texted her, at the same time uploading a brazen post to Facebook that he was about to "do some crazy sh.t".

But the woman received neither warning, and was still asleep in bed with her new lover - one of Robinson's long-time friends - when her jealous ex burst into her house 30 minutes later.

Robinson pounced on the pair where they lay, pinning them both to the bed before throwing a series of punches at his former friend's head and body. The woman was also hit several times as she unsuccessfully tried to stop the assault.

Her intervention eventually allowed her new lover to briefly escape by jumping out the bedroom window into the rear yard.

However, Robinson quickly followed, grabbing a hammer from nearby and using it to repeatedly hit his love rival in the head and body, ignoring the man's pleas for him to stop.

The woman said a few moments later she heard her lounge room window smash and came out to find Robinson, covered in blood from head to toe, standing in the hallway.

"Look what you made me do," he said, unwrapping a makeshift bandage from his forearm to expose a gaping wound that began squirting blood.

He then went to the front porch to wait for police, while the woman went out to check on her boyfriend, expecting to find him unconscious in the backyard.

However, he was not there, and it was later discovered he had jumped the rear fence and taken refuge in a neighbour's house.

Robinson initially blamed his arm injury on his former friend when police arrived, but officers quickly established that Robinson had inflicted the wound on himself.

The 25-year-old was taken to Shellharbour Hospital and later transferred to a specialist hand clinic in Sydney for emergency surgery.

The woman was treated for minor cuts and swelling around her head, while her partner was hospitalised with lacerations to the head and a fractured wrist.

Robinson was discharged from hospital on Christmas Eve and taken into police custody, where he was charged with a host of offences and remanded in custody.

He pleaded guilty to wounding with intent to cause grievous bodily harm during an appearance in Port Kembla Local Court this week via video link.

The case was adjourned to the NSW District Court next week when a sentencing date will be set.