Months before Rachelle Yeo was stabbed to death, the man accused of killing her allegedly demanded to know her new address and threatened to tell her colleagues she was promiscuous.
Ms Yeo and married colleague Paul Darren Mulvihill, 44, were having an affair but when it ended, their relationship soured dramatically.
He is accused of murdering the 31-year-old in her North Curl Curl home in Sydney's north in July 2012.
Kim Blowers, who described herself as one of Ms Yeo's best friends, gave evidence at his murder trial on Monday.
Ms Blowers said Ms Yeo had ended the relationship and when she told Mulvihill she was moving to an apartment, he demanded to know the address.
"He asked her to show him on the computer where she would be living," Ms Blowers told the Supreme Court.
Ms Yeo said Mulvihill became upset when she did not tell him and threw her laptop across the room, Ms Blowers said.
In another instance, Ms Yeo told her friend that Mulvihill asked her to go into a conference room at their work.
"(He told her) he was going to take her down," she said.
"He was going to show her text messages ... he was going to tell everyone she was a slut.
"She was having nightmares.
"Seeing him made her have panic attacks."
Ms Blowers said Ms Yeo told her a card with a picture of a velveteen rabbit with a peace sign on it was left at her work desk and she believed this was from Mulvihill.
Another friend, Sarah Arkins, said Ms Yeo felt "extremely threatened" by Mulvihill's constant phone calls and emails.
Ms Arkins told the court that he had told Ms Yeo "I'm going to ruin your life" and she feared for her career prospects.
The court also heard that Mulvihill had told a colleague that he hoped they would start a life together but when their affair ended he felt Ms Yeo had got off "scot-free" when she started to go out with someone new and he was still with his wife.
After confessing the affair to the HR department of the company Ms Yeo worked for, the pharmaceutical giant Sanofi Aventis, HR staff told her she could work from home if Mulvihill was working from her office.
A colleague often walked her to her car and she was seeing a therapist, the court heard.
Mulvihill has pleaded not guilty and says he was acting in self defence when he fatally stabbed her.
The trial continues on Tuesday.