At least old-fashioned philanderers knew where they stood. For them, only an extramarital affair was considered cheating. In the modern, digital age, however, it takes an awful lot less to wreck a relationship.
Welcome to the world of "micro-cheating".
According to academic Martin Graff, all it now requires is the click of a computer button for a partner to be considered unfaithful. "Micro-cheating" describes behaviour that falls into a grey area between friendly interaction and infidelity. Examples of micro-cheating include checking the social media accounts of former partners; sending emojis such as hearts and flowers to people other than partners; and saving mobile phone contact details of a friend of the opposite sex under a false name.
In short, showing a high level of "digital" interest in someone outside the existing relationship can constitute micro-cheating.
"It can be something as simple as repeatedly 'liking' someone's posts on Instagram or commenting on someone's Facebook," says Graff, a reader in psychology at the University of South Wales. "So much of human relationships has moved online," he says, meaning couples now have to make decisions about what is acceptable online that they didn't have to make 10 years ago.
"Is sending a heart in a Facebook message being unfaithful? Or is it micro-cheating?"
Other actions that can be considered micro-cheating include frequently checking someone's Instagram, messaging someone without your partner's knowledge, adding a former lover on the messaging site Snapchat, or tagging someone in a post as part of an inside joke.
"Secrecy or covert communications are often, but not always, a sign of micro-cheating," Graff says.
A study published by Monica Whitty, another British cyber-psychologist, found that sharing emotional and intimate information with another person online elicited higher ratings for judgments of infidelity than viewing pornography.
Critics of the term micro-cheating say that the concept encourages controlling behaviour and the surveillance of online communications.
"Melanie Schilling, an Australian psychologist, told The Huffington Post: "Allowing micro-cheating to continue can set up a relationship pattern that undermines you and enables your partner to have their cake and eat it too."