Infidelity is a well-researched area of human behaviour Mr Hayward said, with infidelity rates varying from below 10 per cent to 40 per cent, and males typically the worst culprits.
But he said 36 per cent was "really quite high" and likely to have a significant impact on relationships.
"The more transparent we can be with each other, in a way we can continue to respect and value each other, generally the stronger the relationship," he said.
"Most people would want to know if their partners were having a sexual or romantic liaison with another person."
The Colmar Brunton survey found that 81 per cent of adults admitted cheating of some kind, including 22 per cent in the workplace.
And not only are adults cheating on their partners, but they are lying to them too.
Almost a quarter of 280 adults aged over 30 surveyed online in December had lied to their partner - with almost three-quarters feeling guilty about it despite the large majority (84 per cent) saying it was justified.
Lying to avoid hurting someone's feelings was the most excusable lie, the poll found, with only seven per cent of respondents saying this was never okay.
Dr Cate Curtis, senior lecturer in psychology at Waikato University, said while a person's moral code is often shaped by their parents, they can change throughout life.
"All those people we come into contact with over the years will have some influence on the make-up of our morals," she said.
Lying, especially everyday 'white lies', are often thought of in an altruistic manner.
"Sometimes we don't tell people things because it might upset or distress them," Dr Curtis said.
"It can be a matter of weighing up the pros and cons - would it be worse to tell the truth and have your partner upset?"
The survey also found 60 per cent of adults have stolen something, with almost half admitting to shoplifting.
"These results mirror what we found among young New Zealanders and are concerning," said Spencer Willis, leader of the study, which has a maximum margin of error of 4.4 per cent.
Children are taught basic "black and white" principles, according to Dr Curtis, like "stealing is bad".
But as people grow up, the lines of morality can become blurred.
"Some people develop more of an acceptance of the grey area than others ... and it depends also on more complex ideas of justice and fairness.
"If you're in a workplace where you feel valued, well-paid, well-treated, then you're probably less likely to engage in any petty theft to kind of even things up a bit."
Despite admitting the bad behaviour, 91 per cent of adults were satisfied with their personal ethics and character, while admitting lying, cheating and stealing hurt one's character.
More than felt they were better than most people they know.
