SEX - always an interesting topic and a challenge to write, I agree. For me, of contemporary writers, Alan Hollinghurst does it well in The Line of Beauty( though I dont have a copy of the book to hand as I am in Buenos Aires at the moment); Ian Mckewan too - in a very different way, capturing the awkwardness of it in On Chesil Beach. In my own writing I learned a difficult lesson the hard way .My novel Sweeping Up the Village is essentially centred around the development of an affair between my protagonist and the other main character; plenty of opportunity for writing about sex then...in very early drafts last year, when I started to think about the development of this main relationship in my novel I wrote lots of (very bad) sex scenes, most of which nolonger exist or have been completey transformed in their re writing. The key is for me comes back to show and tell - its important that I include some sex scenes to describe the passion and the physicality, after all here are two lovers engaged in an intimate relationship and I want to bring the reader in and up close to share their turn ons and their pleasure of it. BUT... and here is the caveat, its about how much detail and what to leave out as much as what to put in. And it also depends on what the scene is doing in terms of showing the reader(I agree with Emma on this) ; is it early raw animal attraction or naked lust? Is it an emotional tension eg a shift - from being just sex to something more(love, obsession, uncertainity) or is the sex incidental to the overall purpose of the scene , and just needs a passing mention.Like in everyday ordinary life sex happens but its what signifcance is attached to it and by whom and what are the consequences of it happening that matter to me as a stortyteller. Its about quality not quantity- like most things. I am finding myself often using the close third person POV from one characters perspective for most of the scene , to so build up of tension and then I often finish the scene with a shift to the other characters perspective ( but again in close third person POV, as this is the style I am utilizing for this project) - just for a paragraph or even only a couple of lines, so as to underline/emphasize the impact of what has just occured in the scene on the other character(usually my protagonist).The consequence in other words is more what I am after , when I think about writing sex.
I've just remembered another couple of good reads for examples of the art and skill of writing sex and dare I say it the 'L' word. Both novels I would absolutely recommend also because they are both fabulously good reads.
The Great Lover by Jill Dawson
Giovanni's Room by James Baldwin
oh yes, and there are passages also in After You'd Gone by Maggie O'Farrell which do it for me very well too.Hope this helps!