I used to have a thing for diamonds. Maybe it was too many afternoons eating popcorn and watching old VHS movies — Marilyn in the pink dress; Audrey in the oversized sunglasses — or maybe it was just the fairy-tale scenario that little girls seem to be steeped in since birth. In any case, I brandished my great-grandmother’s single solitaire diamond with pride through high school and college, until the day my husband and I decided — on a whim, after two weeks of knowing each other, at the ripe old age of twenty-five — to get married, and it became my official engagement ring. I’m still pining for the…