My wife's sister wanted something--and knew how to get it.

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She caught me staring, for about the fifth time, at her cleavage. Lauren, my wife's sister, just gave me a "you're-a-naughty-boy" and continued slicing tomatoes for the salad.

Lauren and my wife, Abby, are very close. Since only 14 months separate them, their sisterly relationship also took on a very close, friend-like quality. When I first started dating Abby five years ago, it would have been easy to mistake Lauren for an inseparable friend rather than a younger sister because of their easy, natural connection with each other.

My wife is lithe and willowy, with a smooth grace to...