As an author who writes contemporary romantic suspense, sexual tension is as important to the story as the suspense plot. Sure, I let them fool around here and there, but there's always a twist that delays their satisfaction--like a murder, psychological torture, dangerous secret, nutty ex, general mayhem...you get the idea. Just like with the suspense plot that needs to keep the pages turning with one twist after another, it's my purpose as an author to make the characters squirm for as long as possible.
Sexual tension is underrated, both in life and in writing. There needs to be a realistic build up that doesn't cross the line into frigidity or hostility. After all, both in reality and in fiction, the point is to fuel interest not kill it in its tracks. When writing sexual tension, it's important to treat it like you do the natural progression of the plot. Keep it real, don't force it, let it flow. (That works with real life, too.)
Once the time comes for consummation--KaBoom! Light that baby on fire. Don't hold back. The point of the build up is satisfaction. Can the tension remain after the big bang? You bet, but it requires a bit more effort. Just be conscience of that.
Flirting is good for the soul--in real life and in writing--yet seems to be forgotten after the botta-bing of an orgasm. Seduction is a sensuous game that should be savored, no matter what stage the relationship is in. That's what romance is all about--wetting the lips with a teasing kiss, whispering a promise of what's to come and keeping up with the twists and turns that come along.