Audrey Mahon has forgiven her husband David for unlawfully killing her son Dean three years ago but says she has not "forgotten" what happened.
Mrs Mahon said she could not disagree with the jury's verdict because her husband had produced a knife unlawfully.
David Mahon (45) was found guilty of the manslaughter of his stepson earlier this month.
He will be sentenced by Ms Justice Margaret Heneghan on Monday week. Mahon had denied murdering Mr Fitzpatrick on May 26, 2013, a day after the deceased interfered with his bicycle to annoy him.
He had claimed that father-of-one Mr Fitzpatrick walked into the knife he was holding and his death was an accident.
His legal team argued that Mahon's account of what happened was not contradicted by the scientific evidence.
However, it was the prosecution case that Mahon was drunk, angry and agitated and he stabbed his stepson, before fleeing the scene and leaving him to die on the street.
Dean Fitzpatrick was the older brother of teenager Amy Fitzpatrick who went missing in Spain in 2008.
The 23-year-old received a single stab wound to the stomach outside the apartment his mother Audrey shared with Mahon at Burnell Square, Northern Cross in Malahide.
Earlier this month, a jury of six men and six women took eight hours and 16 minutes to reach a verdict that Mahon was not guilty of murder but guilty of manslaughter.
During the sentence hearing yesterday, victim impact statements from Dean's dad, Christopher Fitzpatrick, his mother, Audrey Mahon, his girlfriend, Sarah O'Rourke, and his four-year-old son, Leon, were read to the court.
In her victim impact statement, Audrey Mahon, David's wife and Dean's mother, said her life had become a living nightmare since his death.
She said that, like all mothers, she had a "special bond" with her son, and although he had his problems, she recalled his "cheeky grin" and "heart of gold".
She said she had lost both her children and did not think she was strong enough to cope with losing her husband.
Mrs Mahon said David had also lost everything, and he had done everything in his power to find Amy. Mrs Mahon said her husband had supported her through her illness, through two resuscitations, often literally picking her up off the floor.
She said that "nothing can compare with the tragedy of Dean's loss".
She could not disagree with the jury's decision, she said, because David Mahon had produced a knife unlawfully.
Mrs Mahon further said she has "forgiven Dave but has not forgotten" what happened, adding that Mahon will "always be my husband, carer and my best friend".
Dean's dad, Christopher Fitzpatrick, said his son took his first breath into the world in March 1990, and he was "so small and precious" and he was so "full of joy" to have a son.
He said he will never get to see Dean enjoy his own son Leon growing up.
In his victim impact statement, Mr Fitzpatrick said his daughter went missing in Spain in 2008 and his "world came crashing down again" in May 2013 when he had to identify his son's body in Beaumont Hospital.
He said that doctors told him they had done all they could but the stab wound was so deep they could not save him.
He said Dean's death has taken its toll on him, and he had been hospitalised due to stress.
Mr Fitzpatrick also said Audrey Mahon had tried to exclude him from Dean's funeral and he had been forced to go to the High Court so his son could be buried in his own plot.
He said he hoped Amy would eventually be found alive but he could have no such hope for his son. He also said there were no words to describe his "pain, anger and despair".
Mr Fitzpatrick said that all he now has of Dean is "visits to his resting place".
Ms Justice Margaret Heneghan said she will impose sentence on Monday, June 13.