Adele Stubbs had been out on "one of the best nights" with Daniel Humble before he was killed by youths near an underpass in Cramlington as they made their way home last May, jurors have heard.
A court heard Mr Humble, 35, had caught the attention of his killers because they thought he looked like Ant from the Geordie presenting duo and had jokingly asked for his autograph.
It is claimed after an initial exchange, where Mr Humble had responded "good one lads" to comments about his resemblance to the star, he was "surrounded and attacked" by seven teenagers and suffered a catastrophic injury to his head.
The deadly attack, involving punches and kicks, lasted around just 15 seconds, it is claimed.
Ethan Scott, 18, of Chester Grove, Blyth, Alistair Dickson, 18, of Hawkins Way, Blyth, Izaak Little, 18, of Blackthorn Drive, Blyth, Bailey Wilson, 18, of Mitford Avenue, Blyth, Kyros Robinson, 18, of Woodside Avenue, Seaton Delaval, and two youths who cannot be named, all deny murder.
They are being tried by a jury at Newcastle Crown Court.
Jurors have now watched a video recorded police interview with Miss Stubbs, who said they had had a "really nice night, chatting about the future, life, our plans" before the fatal trouble.
She said: "We had a really good night. Next think I remember is a group of lads either side of the underpass."
Miss Stubbs, who is a nurse, told detectives she did not have a clear memory of what happened in the underpass but remembered shouting "get off him, get off him".
She said: "It just went from zero to 100 so fast.
"Next thing I remember is up on the grass. I got to him and he was out, blood trickling from his mouth.
"Instinct kicked in and I knew something was really wrong. I started CPR. I couldn't look at his face because I knew.
"I was shouting what the 'f' have you done to him.
"He wasn't breathing."
Miss Stubbs said she must have rang 999 but may have then passed her phone to someone else while she performed CPR.
She added: "I heard sirens. I remember feeling relieved someone was coming to help me.
"The technicians arrived and I just lay back and collapsed."
Miss Stubbs said she was taken to a police vehicle and added: "He was in the ambulance and the ambulance wasn't going. I was screaming 'why aren't they going' and she said they were still working on him."
Miss Stubbs said she provided police with the contact details for Mr Humble's mum and her own family and said: "At that point I was in so much shock."
Miss Stubbs said the families went to the Royal Victoria Infirmary, in Newcastle, and they were told scans had shown Mr Humble had a "devastating brain injury".
Miss Stubbs said the night out had been the couple's first since lockdown restrictions eased and said it had been "one of the best nights, planning our future".
During police interviews of the defendants, it was claimed Mr Humble had pushed and or punched one of the youths first.
The trial continues.