The woman needed to go to Southampton General Hospital to have a titanium plate fitted to her fractured eye socket.
Cameron Street, 21, denied the charge, which the court was told arose after he and the woman had returned from an evening at La Couture Inn pub.
The victim had said she went with Street into his bedroom and an argument broke out which led to him hitting her with a carrier bag full of rubbish and then punching her in the face.
Street denied the assault had taken place and said the woman had stumbled while following him up the stairs and he had seen a red mark on her face.
He accepted that an argument had occurred, although for different reasons than the woman had claimed, and she had accused him of taking cannabis from her handbag. He claimed that she had bitten him on the arm, but the woman denied this.
After Street left the room to have a cigarette the woman called the police to report that she had been assaulted, a recording of which was played to the court.
Crown Advocate Jenny McVeigh, summing up the case for the prosecution, said the jurats could be sure of several things – that the complainant had blood on her face from her nose, as seen in the police camera footage; that she had made a 999 call to the police, which had been played to the court, saying that she had been assaulted; and that she had sustained an injury to her eye socket that required her to go to Southampton for surgery.
It was also telling that one of the witnesses who had seen the victim at Street’s home and who also followed the couple upstairs could not say if the woman had fallen on the stairs.
For the defence, Advocate Sam Maindonald cast doubt on the woman’s account of events, and said that it seemed odd that while the woman had accepted that she was quite drunk and Street had helped her up the stairs at his home, she denied that she had fallen.
Other members of Street’s family had gone into his room to talk to the woman and one said she had not seen any sign of an attack, but was there when the woman had bitten Street on the arm – something which Street said she had done playfully in the past, but which was harder than usual this time.
Street had been with the woman for about three years and she said that the relationship had been good but ‘on and off’.
But the defendant’s mother had said it was toxic.
She added that had she thought her son had attacked the woman, she would not have given evidence for the defence and would have told police what he had done.
Judge Catherine Fooks said it was for the jurats to decide what weight they gave to the different accounts of events given and to the inconsistencies in testimonies compared to statements given to police at the time.
After deliberating for an hour, the jurats returned a unanimous guilty verdict. Street was remanded in custody and will be sentenced early next month.