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 an unfettered 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 murdered his wife to get her out of the way.
Ms David told Justice Ian Harrison that there was no committed relationship right away when JC moved into the home but that this had developed over time.
"Your Honour could not accept that she moved into the matrimonial bed as the wife, so to speak."
Dawson previously 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 dispute, Ms David submitted.
Evidence by Warriewood Childcare worker Annette Leary that Mrs Dawson had bruises around her throat after being grabbed by her husband before a marriage counselling session the day before she disappeared should also be discounted, the court heard.
Not only did this evidence not line up with evidence from other childcare workers that the Dawsons arrived at the centre happy and in good spirits, but there were other inconsistencies in Ms Leary's testimony which made it unreliable, Ms David said.
The trial continues.
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