There's no Ruby story, there never was a Ruby story. She exists, somewhere out in the world, but it's not like meeting her is a goal of Lecan's. Reuniting with Boud isn't really a goal of Lecan's either, I think he figures it will just happen when and if it happens. Lecan has literally never mentioned those characters since the first few chapters/volumes, outside of a couple passing thoughts about each of them.
Eda doesn't stall the story. Lecan's goals are to learn magic, learn potion making, and fight through and clear labyrinths for loot and self training. He actually doesn't do any of those until after he actually meets Eda, and he learns only the beginnings of magic and potion making before taking on Eda as a disciple. His first labyrinth clear, which was solo, happens after he starts teaching Eda. Eda as his student is actually a plot device to force him to interact with others. She is pretty useful to have around as well.
That said there's a lot of chapters in which she's not around at all, like when he does the solo Labyrinth clear (30 floors), or the whole time he does the Labyrinth of Swords with Arios (120ish floors.)
The only thing Lecan doesn't really want to do that might be stalling the story is go to the Royal Capital, and that's not Eda related at all. He's just afraid of Yakulbend, I think because Shira said that Yakulbend would be interested in meeting him. Or maybe he's instinctively avoiding something else in the capital, I'm not entirely sure myself.