This morning I was thinking about what common theme is contained in all romance novels of any sub genre. What I came up with is longing and frustration of that longing. The protagonists desire someone seemingly outside their grasp and spend most of the book fighting desire. Sometimes there are external forces keeping the lovers apart, but I believe the most gut wrenching novels are ones in which the protagonist(s) are basically punishing themselves by denying what they crave. Isn’t it so satisfying to see the steps of their journey as they falter their way to a happy ending?
I believe romance is such a popular genre because everyone has experienced a longing for something (or someone) that seems impossible to achieve. Maybe a high school crush that never came to fruition. Maybe something more current. But the sheer need which must be denied for whatever reason is such a basic, primitive thing. Hang any plot around it you want, reaching for something just beyond reach is the crux of romance. IMO.