A 61-year-old woman was slashed to death by her 52-year-old boyfriend who allegedly jumped from their Brooklyn apartment in a likely murder-suicide that came after years of abuse that included taunts over her weight, cops and friends said.

Cops responded to a 911 call at fourth-floor apartment on Sixth Avenue near 53rd Street in Sunset Park just after 2 a.m. and found Delma Mateo lying in the hallway with cuts to her head, neck and torso with a bloody knife, hammer and screwdriver nearby, sources said.

Her longtime live-in boyfriend Felix Santiago was found on the ground outside of the building, with a knife nearby, according to sources. Both were pronounced dead at the scene.

Mateo had faced verbal abuse from the man, whose young son committed suicide and jumped from a different window in the same apartment several years ago, neighbors said.

“Every day he abused her, he would say she’s no good, she’s a heavy person – so she had the surgery to lose weight,” said Joyce Velazquez, who described herself as the Mateo’s best friend. “He used to tell her she looked like 90 years old, she just got her breasts done.”

The victim, who was from Puerto Rico, had lost an estimated 130 lbs. since the surgery roughly three years ago, Velazquez said.

Santiago suffered from schizophrenia and was known to drink and pop painkillers, according to Velazquez.

“He used to tell her all the time that he’s going to kill her and then kill himself,” she said. “She was a wonderful woman. She used to treat him good, she was very scared of him. He used to treat her real bad. He hit her. One time he tried to choke her.”

Santiago’s teenage son threw himself out of a window in the same apartment several years ago, neighbors said. Santiago gave his car to a nephew and gave his son a cellphone and a bunch of cash he had stashed in the apartment the night the carnage leading Velazquez to urge Mateo to leave in a phone call, the friend said.

“She was telling me that something is wrong,” Velazquez said. “I told her ‘You need to leave tonight. He sounds like he’s going to do something bad. He used to always say that he’s going to kill her. She said ‘I’m scared.’ I asked her ‘do you want me to call the police?’ She said ‘no, because it’s going to be worse.”

“He’s planning something. I told her to come to my house,” the tearful friend added. “He wants to kill you. She said, ‘you think?’ I said ‘yes. He’s giving all his money away, he gave his car away and was talking all these things. He’s going to kill you tonight. Please I beg you come to my house. I can ask the police to take you some place. I don’t want you to die.”

Yamais Peña, who lives on the second floor, said he called the police over alleged abuse by Santiago several times, and called on Thursday as he heard Mateo shouting for help.

“Last night she was screaming like crazy, like she need help, call the police. Right away I did, and they come in five minutes. I opened the door for them, and I said, hurry up because she’s screaming like crazy, he’s gonna kill her.”

“The last word that she said, ‘call the police, help me somebody.’ She’s screaming, it’s in my head right now. ‘Help me, somebody call the police.’ I’m so mad that I can’t run over there.”

Cops responding to the 911 call knocked on the door but were told there were no issues by a man inside who refused to open the door, sources said.

After interviewing a neighbor who said they heard loud noises from the apartment, cops busted in through the door and found the bloody scene inside.

While police preliminarily believe the incident was a murder-suicide, the investigation is ongoing, cops said. 

Authorities have not officially identified the pair, pending family notification.