Jared Remy, 35, was sentenced to mandatory life in prison without parole for killing Jennifer Martel, 27.
Remy admitted he killed Martel on Aug. 15 at their Waltham apartment and said he wanted to take responsibility for what he had done.
He described himself as "the bad apple" and called Martel "an angel," but he also appeared to blame Martel.
"I would like you to know that I always told Jen she could leave but don't threaten me with my daughter," he read from a handwritten statement. "That night, Jen had a knife in her hand and threatened me with my daughter, so I killed her."
His father, a former Red Sox second baseman who has been a color analyst on team broadcasts on the New England Sports Network since 1988, was not in court. Remy's lawyer, Edward Ryan Jr., said Remy had asked his parents not to attend the hearing.
Remy defended his parents against criticism leveled at them since Martel's killing and a Boston Globe article earlier this year that detailed Remy's long criminal record and minimal punishment.
"I would like to say blame me for this and not my family," he said.
Remy said his family members did everything they could to help Martel, who he said "helped me clean up my act" but ultimately could not cure him of his "love of drugs." Remy was referring to his use of steroids and painkillers, his lawyer said after the hearing.
He also said, "If you ask my family, they'd rather have me dead than her."
Remy, a former Red Sox security staffer, was fired by the team in 2008 during a steroid investigation.
Besides the murder charge, he pleaded guilty to assault and battery and violating a restraining order. He also pleaded guilty to assault with a dangerous weapon for lunging at a man who tried to help Martel.
Assistant District Attorney Lisa McGovern said the attack came minutes after Martel changed her status on Facebook to read "in a complicated relationship." She said it is unclear whether Remy saw her posting, but shortly afterward, a neighbor heard the couple's young daughter scream.
The neighbor said she saw Martel crawling on the patio outside their apartment, with Remy behind her, and heard her say, "Help me, please help me," McGovern said. Three neighbors tried to stop him, but he fended them off, the prosecutor said.
Remy stabbed Martel in the throat, legs, arms and torso and punched her in the face, McGovern said.
Martel's parents, who attended the hearing, said in a statement read by an attorney that they hope to help others recognize the signs of domestic violence. They said Remy would call Martel repeatedly in what they now see was "more like an obsession than love."
The family also asked for privacy for themselves and the Remy family.
"Together we will do our best to raise our granddaughter as her mother would have raised her," they said in a statement read by a family spokeswoman. Martel's brother and sister-in-law are raising the girl.
Remy was initially arrested Aug. 13 after he allegedly pushed Martel into a mirror. He was released on his own recognizance and stabbed Martel on Aug. 15.
The case prompted questions about whether Remy's violent history had been overlooked by the criminal justice system. It led state lawmakers to propose an overhaul of the state's domestic violence laws, including new bail guidelines and tougher penalties for abusers.
Also, an independent review criticized prosecutors' handling of abuse allegations against Remy.
Since Remy has been in jail, he has been accused of attacking another inmate, throwing hot coffee in his face, hitting him with a plastic chair and punching him.
Remy's family released a statement after his guilty plea had been entered:
"We continue to be heartbroken over Jenn's death. That will never change. No words can express the sorrow we feel for the Martel family. We are now focusing our attention on our grandchildren and doing what is best for them."