Generally speaking... there isn't one.
In the first season, Jimmy expressed an interest in Lois' sister and did on one occasion ask her out, but nothing was ever said about it after that.
In the silver age of comics, there was a lot of default Lucy and Jimmy pairings, and they were sometimes considered going together (when it was convenient to the storyline). In the last twenty years that has not been the case. Lucy is currently married to Ron Troupe, another reporter at the Planet, and they have a child. She has not appeared in any of the comic book storylines for quite some time.
Tank (who never cared for Lucy getting pregnant out of wedlock in the comics)
