Nathan West has been sentenced to 20 years for murdering Dale Cheney.
The man who murdered a 17-year-old stranger in an uncontrollable, jealous rage because he was staying at his girlfriend's family home has been jailed for 20 years.
Supreme Court Justice Elizabeth Curtain said Nathan West, 21, had cruelly ended the young life of teenager Dale Cheney in "a senseless, self indulgent act" because he feared losing his girlfriend.
West, of Sunbury, stabbed Dale once in the back with a 33cm kitchen knife on the night of Sunday, September 30 last year.
Murdered: Dale Cheney
"This was as pointless and senseless a death as one could imagine," Justice Curtain said.
"This was truly a gratuitous act of extreme violence."
The judge said Dale had only been 17 years old, was looking forward to getting his driver's licence and was on the threshold of his life when he was killed.
West, who had had mental health issues since he was 16, had been involved in a volatile, on-again, off-again relationship with Melanie Johns for three years when he killed Mr Cheney. He had never met Mr Cheney before killing him.
Justice Curtain said the relationship between West and Ms Johns was marked by jealousy and immaturity on both sides.
The judge said it was concerning that West still believed he would be able to continue to have a relationship with Ms Johns when behind bars. She had been visiting him in prison before being banned by court order.
The couple had not seen each other for several weeks before Dale's death but had been in constant contact on the phone.
On September 22 last year, Ms Johns' father went interstate on holiday and left Ms Johns, now aged 20, to look after their Banksia Court, Sunbury home.
Ms Johns had several friends staying with her while her father was away, including Corey Semmens and Dale.
West became extraordinarily jealous when he found out that Corey and Dale were staying with Ms Johns.
Mr Semmens, after being threatened by West, told him he was having sex with Ms Johns.
West told friends he was going to stab Mr Semmens.
Having possibly taken both cannabis and ice, West drove his mother's car to Ms Johns' home at 8.45pm on September 30 and sent her 20 text messages and called her six times asking her to come outside to talk to him.
Ms Johns and Dale eventually walked out to the car and told West to leave.
When West returned a short time later, Dale was outside in the driveway near his car before he was stabbed.
West drove off as Dale fell on to his back and died a short time later.
West told friends later that night how he had stabbed Dale and "the knife went in so easy".
"I didn't expect it to go right through. I'm going to jail for sure. He's dead. I've definitely killed him." West said.
West told a psychologist after his arrest how he still believed that one day he and Ms Johns would get married.
He was jailed for 20 years with a non-parole period of 16 years.
As Justice Curtain announced the sentence, West's mother collapsed in court and began sobbing.
West told her, "I love you so much mum," as he was being led away.