1. You're subconsciously unavailable
Maybe you're at a stage in your life where a committed relationship isn't going to fit in.
"Sometimes what can happen is that unconsciously you're not really wanting a relationship, full time, right now," says Fuller. "It might be a stressful time in your life with study or work, or you're ambivalent about wanting to marry or have children, so having a relationship with an unavailable person is much easier than facing those issues head on."
2. You're attracted to bad boys
It's the reason fireman Cam probably didn't win The Bachelorette - he's just too lovely *sigh*. Chasing after bad boys - be they the aloof, noncommittal type or the out-of-bounds married man - is a common pitfall.
"These women find the nice men boring, the nice single men who want to get married or have kids, they think they're boring and want a bit of excitement and intrigue," says Fuller. "Often married guys give them that."
3. You're addicted to drama
Ever wished life was a movie? An affair offers all the nailbiting plot twists, adrenaline and allure of a rom com, minus - more often than not - the happy ending.
"It's all clandestine and intense and you never know when you're going to see them and there's the threat of being discovered, which gives you a thrill, so the whole thing takes on the feel of a movie that you're the star of," explains Fuller. "What makes it work is the fact that you don't have to wash his dirty underwear."
4. There are deeper issues at play
If you've fallen into a pattern of dating forbidden men, Fuller suggests there could be unresolved issues worth exploring.
"I often have questions as to what kind of relationship they had with their father, as sometimes they're replicating a situation where their dad wasn't emotionally available or he hurt them in some way," she says. Think this could be you? Talk to a professional to help you break out of the cycle.
5. The grass is always greener
Feel like the good ones are already taken? Whether we're talking the dream home, the amazing hair or her perfect husband, we all want what we can't have. Jealousy is an ugly beast, and often men seem more appealing in the light of someone else's relationship.
Worse is when the guy in question makes you their confidante before a romantic relationship begins - if he starts telling you his wife doesn't understand him like you do, run for the hills. It's a dangerous position for anyone with heart strings ready to pull on.
How to move on?
Be honest with yourself. "Ask, what function does this man serve in my life?" advises Fuller. "And don't believe that you're just hanging out with him until you meet someone else - you can't meet someone else while you're having an affair with a married man."
If the relationship develops into something serious, it could be best to bring the affair out into the open. "If you've fallen in love with each other, the honourable thing to do is for the attached person to end their pre-existing relationship," says Fuller.
Here's hoping the outcome is more Carrie Bradshaw than Zoe Barnes.