Sure, you can be aware of all the crazy signs she might be cheating on you, but even then infidelity has an uncanny knack of blindsiding you.
Help has arrived, with a new study revealing the most common age at which women cheat on their partners.
The survey also found the average age women get married is 29, which suggests there’s more than a little truth to the seven-year itch.
So what changes after seven years? Do women suddenly get bored of their husbands? Or is it the guy who loses interest, causing her to look elsewhere for love and affection?
Sigurd Vedal, founder of Victoria Milan, thinks it's the latter.
"Perhaps their husband is not giving them the attention and respect they deserve," Vedal says. "Perhaps they still love their partners, but the spark has vanished from their marriage.
"Alternatively, they may have an open relationship, and both have affairs to satisfy their physical needs while still sharing a tight emotional bond," adds Vedal.
What does this tell us about our own relationship? Not much – all people have different needs and desires.
But if you're fast approaching 36, at least now you know to open your eyes to the red flags of betrayal.