It's a tale as old as time: boy meets girl, they fall in love, boy/girl meets different boy/girl, they have an affair, original boy and girl part ways. You've probably come across it at least a dozen times in songs and books and movies - or perhaps your own life if you've ever been cheated on (or maybe even done the dirty with someone else).
It's always seemed that the reasons behind such affairs are many; the person felt neglected in their current relationship, or fell in love with someone else, or, quite simply, made a drunken mistake. Traumatic life events and major changes can complicate the situation somewhat, as can other factors such as kids or marriage - meaning that, most of the time, it can be difficult to pin down exactly why somebody chooses to cheat.
However, according to some people, there are only two different types of affairs.
Tammy Nelson, the resident relationship expert at Ashley Madison, the infamous website for married people seeking affairs, spoke recently with Business Insider in order to discuss the two types of adulterous behaviours exhibited by people in committed relationships.
The first kind, she said, are "can-opener" affairs. "That's when you have an affair because you want out, and you don't know how to end it," she explained. "It's kind of a passive-aggressive way of saying, ‘I want out,' even before I know I want out."
According to Nelson, this kind of cheating is more often performed by women, and is likely to precede the end of a relationship.
Meanwhile, the other type of cheating is more common amongst men, and is more about satisfying an absence in the current relationship rather than looking for a new one altogether.
This second kind of affair, she explained, is "a way of filling that one part of their life that their marriage doesn't. And then they feel like they have everything ... Maybe their marriage gives them physical and emotional validation, but they're not getting the sexual risk-taking that they would want. So they get that from the affair."
Nelson claimed that, in some cases, cheating spouses may only see their other partner as infrequently as a couple of times a year, "but when they do, it's like a full blowout, and then they come back to their marriage and they're perfectly happy."
James Preece, a dating coach, said that this is more common amongst men because they "need much more validation than women, so they will cheat if they get attention from someone else. It makes them feel younger, more virile and wanted."
Women, on the other hand, are more likely to have an end-goal in mind when they have a fling. For them, it isn't just for temporary satisfaction, but rather the beginning of a new relationship (or at least the end of the current one).
To boil it down, then, the two types of affairs are these: ones to end a failing relationship, and ones to uphold a struggling (but otherwise happy) one.