Michael Foran, 33, has admitted killing June 'Katie' Jones but prosecutor Mr Mark Heywood QC told Wolverhampton Crown Court: "It was murder."
The victim, also 33, was knifed at least 21 times at her home in West Bromwich, a dozen of which were in her neck while the rest were in the left of her chest, it was said.
Bruising and pressure injuries showed she had also be asphyxiated while still alive, continued the prosecutor.
Foran claims the fatal attack was caused by a loss of control triggered by fear of violence from Ms Jones or being seriously wronged by something she did or said, the court was told.
Mr Heywood continued: "Anger or loss of temper may well have played their part but not loss of control like that. Evidence shows that in the days proceeding his threats to her were already clear."
Body in the bath
The fatal attack is most likely to taken place on December 10 when Ms Jones was last seen on CCTV coming out of her first-floor flat in Wyndmill Crescent, West Bromwich, and the body lay undiscovered in the bath with a knife lying nearby until New Year's Eve when police broke in at 2am.
She was wearing a dressing gown with a mat and towel also covering part of the body.
Foran phoned his mother Christina in Ireland later on New Year's Eve and told her he was going to be "up for murder," maintained Mr Heywood who continued: "He said he had stabbed her in the neck and heart and left her in the flat.
"He asked if she would put him up if he came to Ireland but she refused and told him to hand himself in."
Mrs Foran then rang her cousin Valery Newman, who lives in Oldbury and told her what her son had said.
Late that afternoon Ms Newman spoke to Foran on his mobile with her phone on loudspeaker as police officers listened and took notes.
He was heard to say: "I'm not handing myself in. I'll go down for life. She drove me mad, nearly 10 years now I'm done, she done my head in."
Escape to Liverpool
Foran had been the last person seen on CCTV leaving the flat where the couple had lived during their relationship when he stepped outside and locked the door around 11pm on December 10. Ms Jones, who had returned with him earlier in the day, was not with him.
She had been due to see members of her family in Malvern until December 12 but never arrived.
Repeated calls to her phone went unanswered and when they contacted Foran on December 17 he said she was out with a friend and would be back around 9pm.
They called again after that but he said she had still not returned, the court heard.
The family became increasingly concerned and reported her missing to police on Boxing Day.
Foran was driven to Liverpool on New Year's Eve by his friend Keith O'Dwyer who claims he did not know there had been a murder, maintaining he was told that his pal had no reason to stay in the area because Ms Jones had left him, it was said.
Foran was dropped off at a £15-a-night hostel in Liverpool, where he booked in under the name Michael, and his picture was later recognised by the manager when it appeared in a local paper.
Foran was arrested on January 5 after being spotted begging with a dog outside a Poundland shop in Liverpool city centre.
He denies murder and 34-year-old O'Dwyer, from Camberley House in Beaconview Road, West Bromwich, pleads not guilty to assisting an offender.