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Could be a Stock Shout-Out to The Pina Colada Song
? Doesn't seem like we've got that specifically on Your Cheating Heart.
This seems a little like Gift Of The Magis Plot, but not quite the same.
I don't think we have it, but it is a rather popular plot twist in older works.
The "Pina Colada Song" version plays out like a subtrope of It Was with You All Along: you try to cheat in order to find your ideal partner, only to realize the person you were already with is your ideal.
It definitely seems familiar, especially if we broaden it slightly beyond cheating couples to include other similar cases. The general pattern seems to be "Alice and Bob think they hate each other, but fall in love (or back in love) when their identities are concealed."
In that generalized case, it also covers the plot of The Shop Around the Corner, She Loves Me, You've Got Mail, et al.
^ That one's already covered by Acquainted in Real Life.
Two characters in a relationship independently decide to cheat on each other, but due to various coincidences (and possibly alcohol) end up unknowingly sleeping with each other. Usually they then "realize" that sex with other people isn't actually different from sex with their spouse, and return to their marriage.
A variation is for both people to place ads in the newspaper's singles column, get an answer, and discover it's their spouse.
Edited by Chabal2