File photo: The findings applied to both men and women, whether or not their relationships were marriages.

London - Wondering whether to forgive a cheating partner? Don’t.

Because people who have an affair are nearly three-and-a-half times more likely to stray in the next relationship, scientists say.

And to add insult to injury, men and women who have been cheated on are more likely to see their second partner have an affair too. One theory is that the brain adapts to dishonesty so the more someone cheats, the easier it becomes.

The study, published in the Archives Of Sexual Behaviour, followed 500 people through two relationships over five years. It found first relationships lasted an average of 38.8 months before they ended, while second relationships were 29.6 months old when the study finished.

Those who had a fling in their first relationship were 3.4 times more likely to do so in the second compared with those who did not stray in their first. Those who knew their partners had had flings in their relationship were 2.4 times more likely to report the same behaviour in their next partners.

The findings applied to both men and women, whether or not their relationships were marriages.