Katie Foreman was in a lesbian relationship with Wendy Evans, the woman who eventually killed her, the one-time boyfriend of both women has claimed.
Scott Field told jurors hearing the case against three people accused of helping Evans kill Ms Foreman that he had received picture messages from the two women showing them engaged in "sexual activity" together, which he described as "kissing and other things". He also recalled witnessing their intimacy first-hand some time around February 2011, when the trio was heading home to Wollongong after watching cage fighting in Newcastle.
He told the court that while he was driving, Ms Foreman and Evans were sexually active in the rear seat.
He said at one stage he pulled the car over and joined them.
"You stopped the car and also engaged in sex with them ... some acts were recorded on a mobile phone?" Crown prosecutor Chris Maxwell, QC, asked Mr Field.
"Some of the acts included you receiving oral sex from both women?"
"Yes," he responded.
The court heard the relationship between Evans and Mr Field began at the end of 2008; however, they'd known each other since childhood. Their relationship fell apart in late 2010 and Mr Field began seeing another woman. However, he maintained contact with Evans, who had introduced him to Ms Foreman while they'd been together.
Mr Field told the court he and Ms Foreman became intimate after he took her for a ride on his motorbike one night in February 2011 and then had sex at her home.
The pair called or text messaged each other daily and had sex "on a regular basis".
Mr Field, a convicted criminal, was returned to custody on March 17, 2011 after having his parole revoked. He said Ms Foreman visited him and they spoke on the phone a number of times in the months before her October 2011 death. He said Evans also called him while he was in jail and tried to visit him once but had not been allowed in.
"Was she upset and angry with you because she'd found out about you and Ms Foreman?" Mr Maxwell asked.
"Yes," Mr Field replied, telling the court when he asked Evans if she'd spoken to Ms Foreman about it, Evans said: "I will never speak to that slut again."
Earlier, the jury heard from the doctor who carried out the post-mortem examination two days after Ms Foreman died. Forensic pathologist Dr Matthew Orde told jurors he found no signs of Ms Foreman being pregnant - a matter at odds with information Bradley Max Rawlinson allegedly told Ms Foreman's cousin, Alicia Gibb, on the day of her funeral.
"He said Katie was pregnant when she died," Ms Gibb previously told the court.
She said when she asked Rawlinson if Ms Foreman had told anyone, he replied: "No, only me."
Dr Orde confirmed toxicology tests on samples taken from Ms Foreman's body returned negative results for amphetamines, sedatives, cannabis, cocaine, codeine, cyanide, methadone and morphine, as well as alcohol.
The trial continues.