Jordan Felton threatened his partner when she tried to leave his brother's home in Burmantofts and chased her with a kitchen knife.
The 19-year-old was the subject of a suspended sentence at the time of the offence, which happened on December 18 last year.
Danielle Gilmour, prosecuting, said the defendant had an argument with a woman on his girlfriend's phone and threw it against a wall, smashing the screen.
The prosecutor told Leeds Crown Court the victim rang her brother and asked him to meet her.
Felton grabbed her and held a knife to his wrists and throat. He said: "If you go out that door, I will slit my throat in front of you."
The victim's brother rang the police.
Ms Gilmour said the pair then chased the victim, with Felton shouting: "If you leave, I will paralyse your mum" and "I will shoot your dad".
When the victim arrived at Felton's flat in Ferriby Towers, he was already there and told her: "You're not getting your stuff, I'm selling it all."
Felton was arrested at his flat after being "confrontational" towards police officers who were called to the incident.
Felton, of Ferriby Towers in Burmantofts, pleaded guilty to common assault, criminal damage, possession of an offensive weapon in a public place and breach of a suspended sentence.
Felton has been in custody since his arrest on December 18.
Fiona Clancy, mitigating, said her client used spice at the time of the offence.
Ms Clancy said she believes Felton has undiagnosed mental health issues.
She said: "He has found being in prison very, very difficult."
Judge Mushtaq Khokhar sentenced him to five months in detention, suspended for 18 months.