It's simple. Which of the many love stories in all the ST series really spoke to you?
I would have to say the first one, because of its tragic overtones. I'm speaking of Captain Christopher Pike and Vina, the lone survivor of the crash-landing on Talos IV, from The Cage
and The Menagerie
Vina's reason for staying, that she was disfigured, was made more poignant by the ending of The Cage
: that the Talosians let her think Pike stayed behind with her. And then, Pike's terrible accident with the Delta Rays gave him a choice, to be with the woman he loved, especially now that they both had so much in common -- both physically maimed.
I just rewatched The Menagerie
and this topic idea came naturally to me. And it's also the first official sequel in ST history, come to think of it.
One more thing: try to limit your favorite love stories to canon, eh? So 'shippers, take a cold shower!