Michael Davis pleaded guilty last month to second-degree murder in the death of Josie Berrios.
He was sentenced to 25 years to life in prison on Friday.
The 47-year-old admitted to setting a fire on a construction site in Ithaca on June 13, causing the death of Berrios.
The victim's family said they were worried about Davis and Berrios' relationship from the start.
Her mother calls the sentencing a bittersweet moment.
"She's gone, and I'll never get her back," said Lorena Berrios, the victim's mother. "She was loved, and as my sister-in-law said, she was wanted, and today we got justice for her."
Davis also waived his right to appeal as part of the plea.