A brandy drinker woke in a police cell after punching his girlfriend and shouting abuse at her.
Since then, Kyrie Michael, 24, has shown "massive remorse and massive apologies," his solicitor told Nottingham Magistrates' Court.
District Judge Leo Pyle heard the incident happened early on Saturday morning after the couple had been out.
When they returned to her home, Michael began to accuse her of being unfaithful, said Sanjay Jerath, prosecuting.
She then felt a blow to her right cheek, which was left painful. She said later: "This is the first time he has hit me. I feel so sad and disappointed that he has done this."
Mr Jerath added: "Both had been drinking. She had vodka and he had brandy."
Michael, of Perlethorpe Avenue, Sneinton, pleaded guilty to assault causing actual bodily harm.
He also admitted being in breach of a suspended prison sentence imposed on June 26.
He was sent to Nottingham Crown Court to be sentenced on July 30. Bail was refused.
Chris Saunders, mitigating, said this was the first time Michael had drank alcohol since going on medication.
"He has no recollection of this incident and it is patently obvious that he is somebody who has regrets in relation to this matter.
"There is massive remorse and massive apologies," added Mr Saunders.
The judge said the crown court would receive a hospital report on the extent of the woman's injury.
"I have to look at the facts of this case and the fact that it was committed within days of the imposition of a suspended sentence," the judge added.
