Jack Gates, 27, flew into a drunken rage after convincing himself that his girlfriend was seeing another man, York Crown Court heard.
During an argument in the street with his partner, he pushed her to the ground and dragged her by her hair, before smashing her head against the pavement, said prosecutor Rob Galley.
“He had both of his hands against her throat and was squeezing tightly,” added the barrister. “She was finding it difficult to breathe.”
As the terrified victim, who was named in court, screamed out for help, Gates - drunk out of his mind on Southern Comfort - threatened to kill her, before snatching her mobile phone and running off, said Mr Galley.
A short time later, at about 1.15am on August 7, police received another call-out from a distressed woman in Beulah Terrace, Scarborough, and this time it was Gates’s younger sister.
When police arrived at her flat, she was bleeding heavily from two “relatively small” wounds to her arm. She was holding a towel around her wrist to stop the bleeding.
Mr Galley said the woman, who was also named, also had what appeared to be a stab wound “or similar type (of wound)” near her left eye.
He said it appeared that some arteries in her arm had been severed, although this could not be proved.
She was taken to hospital and told officers she was worried that her brother might have gone looking for the man who he believed was seeing his girlfriend.
Police found Gates in a garden in Scarborough at about 6.30am and arrested him, added Mr Galley.
He said that between the attacks on the two women and Gates’s arrest, he had sent messages to the named man threatening him with violence.
“The defendant had been using the mobile phone he had taken from his girlfriend and had been sending messages between 2.45am and 3.05am to (the named man), threatening to kill him or harm members of his family,” said Mr Galley.
Gates also sent a Whatsapp message to the man pretending to be his girlfriend, in an attempt to get him to admit that he’d been having an affair with her.
Gates, of Beulah Terrace, admitted assaulting his sister, causing actual bodily harm, common assault against his girlfriend and sending a threatening message to the named male.
He appeared for sentence via video link on Tuesday after being remanded in custody following his arrest.
The court heard that Gates had a lengthy criminal record including battery, possessing a knife and assaulting a police officer.
Defence barrister Taryn Turner conceded that Gates’s latest offences were “disgraceful” and had stemmed from her client’s ungrounded suspicions that his partner was having an affair.
She said Gates had a drinking problem and needed help for mental-health issues.
Gates admitted that a knife had been used during the incident with his sister but claimed he had tried to kill himself and that she got hurt while trying to wrest the blade from him.
“It was a grapple – I had no intention to hurt my sister,” he claimed.
Judge James Spencer QC told Gates: “You have been in court as often as I have because your record is long and varied.”
Jailing Gates for eight months, Mr Spencer told him he would serve half his sentence behind bars and would be released by Christmas, but added: “If you behave like that at Christmas; if you have too much Southern Comfort, you’ll be back here in January.”