Longing in Romance

I think modern romance writers sometimes focus so much on the hot sex scenes that they forget the power of longing in making the audience root for the hero and heroine to get together. Twilight does this very well. How much of that series is about Edward and Bella being apart rather than together? Or think of Gone With the Wind. Or Buffy and Angel.

In The Rose Throne, both Issa and Ailsbet have to deal with longing, though in very different ways.