Mr Stewart was speaking in a Brisbane court about the impact of his son Balin's death before a 19-year-old was sentenced to seven years in detention.
A Supreme Court jury in June acquitted the teen of murder but found him guilty of manslaughter.
Prosecutors had rejected his offer to plead guilty to manslaughter before his trial.
The teen, who cannot be named for legal reasons, was 17 at the time of the brawl with Balin outside the Stewarts' home on Queensland's Sunshine Coast in January 2022.
He had significant animosity toward Balin due to the younger boy's relationship with the teen's former girlfriend, Justice Elizabeth Wilson said in sentencing the teen on Friday.
After receiving provocative videos from the girl's phone, the teenager took a steak knife from his kitchen and drove to Balin's house.
He arrived aggressive and hostile, yelling for Balin to come outside before throwing the first punch.
The girl told the court she first saw the knife after separating the two.
The teen was aggravated, saying, "I'm going to kill him" and refused to leave or put down the knife.
During a second altercation the teenager stabbed Balin in the chest with enough force to penetrate his heart.
The distraught teen repeatedly apologised, with Justice Wilson finding the statements "so raw" and an immediate expression of remorse.
But she found he drove the 5km to Balin's house with the intent to at least cause him grievous bodily harm although it was in the context of provocation.
Justice Wilson accepted the teen thought Balin may also be armed with a knife.
The provocation offered by the videos was sufficient in the context of the teen's toxic relationship with the girl, his animosity toward Balin and his youth, while the drive was insufficient for his passion to cool.
Justice Wilson described as "heartbreaking and harrowing" a statement by Balin's father.
Mr Stewart said the 19-year-old had taken so much from many people because he was jealous and weak in picking up a knife that night.
"All of these lives destroyed and broken in an instant that night," Mr Stewart told the court.
The teen had stolen Mr Stewart's ability to sleep peacefully as he woke daily relieving the night of the stabbing of his son - who would have turned 18 next week.
"I have no peace any more."
The death had destroyed Balin's mother Kerri-Lynn who had been a pillar of strength for the family.
Mr Stewart said it was insufferable seeing autopsy photos of Balin's bruised and battered body during the trial, and watching the teen's "cold, callous and calculating" answers to questions.
"You might pretend to be sorry, you might pretend to be remorseful, you may struggle with what you have done but nothing will bring my son home.
"You've robbed us all. I will never forgive you. Never."
The court heard the teen, who has no previous convictions, had been traumatised when as a nine-year-old he, his grandmother and sister found the body of his mother who had taken her own life.
Justice Elizabeth Wilson handed the 19-year-old a sentence of seven years in detention, ordering he be required to serve half of that term behind bars.
He has been in custody for 90 days since the stabbing and was sentenced under the Youth Justices Act.
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