Another reason is what he calls "safety in secrecy".

"If both people in a relationship want to be secretive about it, then the chances of exposure is limited," says Wilks.

The fact that there is no commitment is another reason.

"There is always no commitment at the start of these sort of relationships or flings.

"No commitment does not only mean not committing to the relationship but also committing in terms of time.

"The single person will have more time on his or her hands.

"This is because the other party would also have to be with their spouse and children, if any."

Another factor that lures singles to this kind of relationship is our innate competitive nature, says Wilks.

"If a single woman sees a happily married couple who are very loving towards each other, she might think: 'He's a great guy and she has him but I reckon I can get him'," he says.