Dina Sharpe had a three-year relationship with Singer
A man who spiked his girlfriend's omelette with sleeping pills, beat her and trapped her by setting fire to her home, has been jailed for life.
Neighbours failed to save Dina Sharpe, 39, who called out for help from her burning flat in Southwark, south London while holding a 17-month-old boy.
The toddler survived but suffered 75% burns, the Old Bailey jury heard.
Stephen Singer, 37, of Southwark, was ordered to spend a minimum of 23 years in jail for the killing last August.
The court was told that Singer had been having a three-year relationship with Miss Sharpe while living with another woman.
Things came to a head last summer when the woman found out and threw him out.
Judge Stephen Kramer said: "You are a controlling person who was prepared chillingly to use aggression and deceit to take control of a complex triangle of your own making."
Stephen Singer was having relationships with two women
The court was told neighbours heard Miss Sharpe's cries from her fourth-floor flat in Charlton House in the early hours of 3 August.
She was also seen at the window holding the child, with flames in the background.
Andrew Munday, QC, prosecuting, said neighbours were able to save the boy, who was found on the bed shielded partly by Miss Sharpe's body.
He said a post-mortem examination found the victim died from brain damage due to injuries on her face and head, and her blood contained traces of sleeping pills which were also found in a glass of wine and half an omelette at the flat.
Police said Singer "viciously assaulted" her when the drugs took effect.
Miss Sharpe's cousin, Deborah Judge, told the court: "To us, Dina died a hero.
"We will never understand why Stephen Singer didn't just walk away."
Outside court, Det Ch Insp Carl Mehta said: "This is an absolutely horrific case and the level of callousness and brutality used by Singer to plan and execute the murder is just unimaginable."
Singer was also jailed concurrently for 20 years for the attempted murder of a toddler and six years for arson.