My Irish Catholic mother loved romantic movies, provided they ended with a kiss before the screen went dark. If things went any further than that, she'd complain, Why can't they leave something to the imagination? I sort of subscribe to her philosophy when it comes to writing sex.
You have to be able to play: this is spontaneous interaction, and it flexes all the creative muscles you need as a writer. And empathy is one of those muscles.
Chekhov used to correspond with aspiring writers, and once he gave this advice to Maxim Gorky when he was encouraging him to pare his wordy sentences: "When someone expends the least amount of motion on a given action, that's grace." The short story, by definition, embodies this notion of grace, because it requires such forceful compression to achieve its effects.
For me, what's compelling about sexuality is the way that desire transforms what we take in through our senses, the ways in which our bodies betray us or rescue us by insisting on their own non-negotiable truths. Anything but frank or pragmatic.