Conor Munro attacked Nicole Jarrett after she poured his whisky down the sink at the supported accommodation in Arbroath where he was staying.
The court heard the attack was carried out in front of staff who did not intervene "for their own safety."
Munro will be sentenced at Dundee Sheriff Court in December.
Depute fiscal Vicki Bell told the court that Miss Jarrett had run from Munro's bedroom screaming, following an argument.
She said: "She tried to leave and picked up his glass of whisky and poured it down the sink.
"He grabbed her by the face and pushed her down.
"She got up and took the opportunity to pour the rest of the bottle down the sink.
"He then pushed her again and, having done so, punched her."
Miss Bell said Munro repeatedly punched Miss Jarrett in the stomach before punching her nose, causing it to bleed.
She said: "He was on top of her, grabbing and pulling her face, and blood was collecting in her throat making it difficult to breathe.
"He put his hand over her mouth and she was continually struggling to breathe."
The fiscal said staff looked out of the office window and saw Miss Jarrett covered in blood.
She said: "They saw him wrap his arm round her neck - she was hysterical and crying for help.
"Staff shouted that help was coming and phoned 999 but made the decision not to open the office door and confront the accused for their own safety."
Munro, 24, admitted the offences, which were committed on 21 September.
Sheriff Alastair Brown deferred sentence and remanded Munro in custody.
He said: "I am considering remitting this case to the High Court for sentence, or imposing an extended sentence myself."
A man who left his girlfriend choking on her blood as he strangled her has been told to expect an extended prison sentence.