So I'm trying to come up with a few ideas, probably to be included in a short chapter devoted to romantic plots and sub-plots, rather than the main adventures. So far I've got
Earth Girls Aren't Easy
When the owner of Titan's main gold mine is killed, his daughter ships out from Earth to take over the family business. Needless to say most of the single men on Titan (pop. 50) are VERY interested, but she has ideas of her own - and a lethally fast trigger finger.
The Best Little Whore-House on Deimos
Speaks for itself, but I suspect not quite the right type of romance (which isn't really the right word)...
The Princess Bribe
While visiting Mars / Venus / some other colony a Russian princess (or whatever) decides that she has had enough of the decadence of Earth and wishes to experience the adventurous life as a pioneer. Our intrepid heroes are hired to make life unpleasant for her, but harmlessly so, with the goal of persuading her to return to Earth and resume her royal duties. Of course things won't be that easy...
Any other suggestions?
Later Just realised that the perfect title for this section is, of course, Love and Rockets