Greg Reardon faced his girlfriend's killer in the dock today as he described his "buzzing level of stress" at finding her missing.
Mr Reardon said he gave Joanna Yeates a cuddle and a kiss before setting off to see relatives in Sheffield on the night of her death.
After failing to get hold of her all weekend, he said he "did not immediately think something was wrong" after returning to find their flat empty on Sunday night.
Concern turned to panic after he found her mobile phone and then keys, he told Bristol Crown Court.
"I kept saying to myself 'She's gone out for the evening and she has forgotten her coat'," Mr Reardon told the jury.
Vincent Tabak, sitting in the dock with his hands covering his face, made no eye contact with Mr Reardon during the evidence.
Mr Reardon told how he and Miss Yeates had been looking forward to watching the final of BBC show The Apprentice on the evening of his return to Bristol.
When asked by Nigel Lickley QC what her plans had been for the weekend, Mr Reardon said: "She had mentioned her plans to finish her Christmas shopping.
"We also had a get-together coming up and she wanted to do some baking."
Having failed to get hold of Miss Yeates after calling and texting her, he said he had returned to find the hall light on.
It had been unusual to find Miss Yeates's boots in the middle of the hallway, he said.
"It was quite untidy," Mr Reardon told the court. "There were clothing, boots and shoes and general paraphernalia."
Mr Reardon said that when he returned home on the Sunday night he he was surprised at how untidy the flat was.
He told jurors he paced around the flat, tidying as he went, and trying to piece together what may have happened.
"I was wandering about," he said.
"I didn't really think there was a big problem. I thought she may well have gone away visiting friends.
"So I thought she may have been away doing fun things, so not having been able to get hold of her phone ... I wasn't sure."
Mr Reardon said Bernard the cat was pleased to see him and wanted to go outside to the toilet. The cat was also hungry and quickly ate his dinner.
Referring to the hungry cat, the clothes on the floor and general mess, Mr Reardon said: "I didn't immediately think anything serious was wrong.
"I was quite annoyed that I had not been told what her plans were and she had not got back to me and I was starting to feel quite worried."
Mr Reardon said he had eaten a pizza from the freezer for his dinner and drank the open bottle of cider he had found in the flat when he got home.
Mr Reardon, who works as an architectural assistant, said he spotted his girlfriend's rucksack on the dining room table and when he opened it he found her glasses, sunglasses, keys and wallet inside.
Her striped jumper, which she had been wearing on the day she was last seen alive, was also in the bag.
Mr Reardon told jurors: "I started pacing around the flat.
"I had this increasing buzzing level of stress.
"I didn't know what was going on, so I walked around the flat and, trying to find out what she might have done, so I went tidying up as I went, trying to find out what she was wearing by looking at what was out.
"I panicked really. It was midnight. It was a realisation that now something is wrong."
Mr Reardon said that he thought his girlfriend had been locked out of the flat with all her possessions inside.
"I started to ring around her friends and my friends in Bristol to try and find out where she was, if she was with them over the weekend," he told the jury.
"I rang all the people she had been in contact with on the Friday night and any of her friends that I could think of that might have seen her."
He also reluctantly phoned her parents, David and Teresa, to see if she had gone home for the weekend or had contacted them.
Mr Reardon said that he found a pair of his girlfriend's earrings in the bedroom.
One was in the bed and the other earring was on the floor under some clothes.
Mr Reardon said that he only found one of the fasteners and that usually when she removed her earrings she left them on the bedside table.
He also confirmed he had seen both Tabak and his girlfriend Tanja Morson passing his kitchen window as they walked down the footpath to their flat door.
Mr Reardon said he had spoken to Miss Morson when the cat had got inside her flat but had never spoken to Tabak or realised he was foreign.