The aftermath of infidelity can cause huge emotional ruptures for even the strongest of relationships. But when one in five British adults admit they’ve had sex with someone other than their spouse, it raises the question: just why are so many people inclined to be unfaithful – and do those who cheat have anything in common? Dr Janine Hayward, a clinical psychologist and infidelity expert, shares five lessons she’s learned from over a decade of working with couples who have navigated – and survived – affairs.