Christopher Michael Dawson could engage in the French national sport of loving two women at the same time, his murder trial has been told.
Continuing her closing submissions on Friday, defence barrister Pauline David said it was normal for a man to have feelings for two women simultaneously.
Dawson, now 73, is accused of murdering his wife Lynette Dawson and disposing of her body in January 1982 because he wanted a relationship with his former high school student, known as JC.
Ms David argued that Dawson could have a long and loving relationship with his wife while having sex with JC, saying the French did it as a national sport.
"I think the reality is a man can love two women at the same time ... It happens that you care about two people deeply. Sometimes you're very torn," she told the NSW Supreme Court.
Dawson acknowledged that his extramarital affair with JC had been hurtful to his then wife but that he had already paid a very heavy price for it, the barrister said.
In an interview with homicide detectives in 1991, Dawson said he had yearned for contact from his wife after she had disappeared in January 1982.
Evidence suggests JC moved into his matrimonial home in Bayview, Sydney soon after Mrs Dawson vanished and was photographed wearing her clothing. However, his legal team has denied any inferences could be drawn from this that he murdered his wife to get her out of the picture.
Allegations Dawson had killed Lynette to start an "unfettered relationship" with JC were roundly rejected as completely illogical because her disappearance forced the couple to take care of his two young daughters rather than being able to spend time together alone.
"(Lyn's absence) created a problem rather than eliminated one because (JC) didn't want to have this relationship with him and the kids... She wanted the children not to be there," Ms David said.
Any alleged financial motive for Dawson getting rid of his wife to retain ownership of the Bayview home was dismissed as well because of the considerable burden and expenses of raising children alone.
The barrister told Justice Ian Harrison that there was no committed relationship right away when JC moved into the home. She had moved in for practical purposes as a babysitter and a relationship had developed over time.
Dawson has claimed he only began a de facto relationship with JC in April 1982. The pair married in 1984 and separated in 1990 amidst a heated custody dispute.
Ms David said her client's marriage to JC was not unusual because he truly thought Mrs Dawson had abandoned the home and moved on.
Evidence of any animosity towards Mrs Dawson could be rejected, the barrister said.
Claims by JC that Dawson had tried to hire a hitman to kill his wife before she disappeared were unreliable because they were first made during the acrimonious custody spat, Ms David submitted.
These allegations were claimed to have had a huge impact on Dawson's reputation, including that they had changed how Mrs Dawson's family viewed him after they met with JC in 1990.
"That is exactly what (JC) wanted to achieve. She wanted to turn the world, we say, against her husband at the time."
JC's stories about the alleged hitman had changed with each recounting, including details such as when it occurred, when Dawson told her his intentions, what Dawson had said, and who else was there, the court heard.
Ms David continued her attack on the police who investigated Mrs Dawson's disappearance from 1998 to 2015, especially former Detective Damian Loone who headed up the team in that period.
The police held a fixed view about Dawson's guilt and ignored evidence which corroborated his statements or showed that his wife was still alive, she said.
"They are lying, Your Honour. They are corrupted. Their attitude to Christopher Dawson was significantly a prejudiced one."
The trial continues on Monday.
