But generally speaking, you can boil down all these affairs into two discrete categories.
That's according to Tammy Nelson, a sex and relationship therapist and the resident relationship expert at Ashley Madison, one of the most popular websites for people seeking affairs. Nelson has been in practice for about three decades, and she joined Ashley Madison recently as an outside consultant.
When I spoke with Nelson by phone, she told me that people who stray typically either want to leave their primary relationship or don't.
People in the first category wind up in what Nelson calls a "can-opener" affair. "That's when you have an affair because you want out," she said, "and you don't know how to end it."
In Nelson's experience, women are more likely than men to have can-opener affairs. "It's kind of a passive-aggressive way of saying, ‘I want out,' even before I know I want out."
Other people having affairs don't necessarily want to leave their primary relationship. Instead, Nelson said, "it's a way of filling that one part of their life that their marriage doesn't. And then they feel like they have everything."
She shared a hypothetical example: "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."
Interestingly, Nelson said some people may only see their affair partner a couple 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".
A (non-scientific) study supports Nelson's observations. HuffPost reported that Victoria Milan, another site for married people seeking affairs, surveyed 4,658 members and found that 69% said they don't think about leaving their significant others.
Meanwhile, couples therapist Esther Perel previously told Business Insider that, oftentimes, an affair has little to do with a person's satisfaction or dissatisfaction with their relationship. Instead, the person may be unhappy with themselves. (Nelson also suggested that some people who have affairs are simply bored with themselves.)
When Nelson sees clients who are having an affair but don't want to leave their marriage, she often hears them say things like, "My husband would never do that" — "that" being some kind of sexual behaviour.
"That may or may not be true," Nelson said of the client's rationale. "It might just be a story that they make up to justify it." On the other hand, she mused, maybe the client is right. "Maybe we can't get everything we need from one person."
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