George Takei was a much better actor than Jimmy Doohan. If there was a reason why Sulu didn't have any love stories, it's lost on me. Maybe George didn't express an interest in that sort of thing and if he'd piped up, Gene would've made it a point Sulu got to kiss up on some Smokin' Hottie. Unless there's a paper trail on this, it's all conjecture, anyway.
I hate the Dr. McCoy love stories, though, and Praise be to Allah, there's only like 2 of them: Nancy the Salt Addict and that Oracle woman. Bones was already a bit old to be Playing the Field, he didn't need no romancing, he was already given plenty else to do. And Spock's romances all had some catch involved.
The Spore Chick was possessed with a plant fungus. When he kissed up Zarabeth, it was only because he was in commune with his barbarian ancestors 5000 years in the past. His betrothed was already with another Man, when Spock returned home, with his raging hormones. Checkov's blondes were out of his league and only were with him, in the first place, because it was in the script. That is, there was no believability factor, involved.
Out of all of them, only Kirk had the normal romances. The ones worthy of remembrance. Like Edith Keeler, with her sexy little accent. And, uh ... who else? That little robot number Leonardo da Vinci introduced him to ...