Trefor Kingdon and Mandy Melzer were childhood sweethearts who got back together decades later after a school reunion.
But early one morning in May 2020 Kingdon stabbed Ms Melzer 11 times with a kitchen knife at their Bendoc home in Victoria's northeast.
Kingdon, 65, then staggered into a room where his friend had stayed the night after catching up with the couple and said: "I think I've killed Mandy".
Hours earlier Ms Melzer, a retired schoolteacher, cooked the trio a three-course Italian dinner. They drank champagne and red wine and played a board game together.
Kingdon attacked Ms Melzer about 3am after she told him she wanted to end their relationship.
His friend called triple zero and tried to save the 63-year-old woman's life by performing CPR until authorities arrived.
But she died on the kitchen floor.
Kingdon on Tuesday faced the Victorian Supreme Court and pleaded guilty to murdering Ms Melzer.
"This is a violent and brutal attack with a bladed weapon on a woman in her own home, where she was entitled to feel the safety and sanctity of that environment," prosecutor Kristie Churchill said.
"This is yet another case of domestic homicide before the court. Women continue to be killed at the hands of their partners."
Kingdon's barrister Rishi Nathwani said the former mortgage broker had no previous history of domestic violence and had never been in prison.
The 65-year-old was guilt-stricken and felt a palpable sense of shame and remorse.
"I know I've caused so much pain to so many people," Kingdon said through his lawyer.
"I know I'll be punished for what I did and that's just and right."
Justice Lex Lasry will sentence Kingdon at a later date.
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