Like many couples, my girlfriend and I agree that Valentine’s Day is a commercial holiday. Last year neither of us wanted to do anything traditionally romantic, like go out for a fancy dinner. We wanted, instead, to do something scandalous.

We had a wish list of activities we’d been gradually checking off, and talked over a few possibilities. We settled on one of my suggestions: We would go to a bar that neither of us frequented, pretend to be strangers, and I would try to pick her up.

We had been dating for eight months, long enough to get comfortable with each other. Getting comfortable is one of the pleasures of being in a long-term relationship: not having to put up a first-date front, getting takeout and watching TV, being boring together. It’s a relief not to have to be “on” — to feel free to be in an unattractive mood or display one of your weird neuroses without worrying the other person will finally realize the truth about you.

But this is also a hazard of relationships: You can take your partner for granted and quit trying to impress. Couples forget how to flirt, or that they’re attractive to anyone else, and get bored — with each other, and themselves. Until the day it emerges that one of them has a whole secret life: an affair or erotic correspondence, a hidden kink, an ex of some unexpected type or gender.