I'd be shocked if it was revealed that Sano was into him at all. Though I think we'll definitely get an Arc where he's convinced of that for a while.
As for the losing heroine thing...
What if he was right? The older sister did like him and was flirting with him, but some kind of circumstances...
Interesting that chie didn't detail what the other girls were doing there... her sugar baby, the middle schooler she bought and turned into a maid, the gambling addict, the masochist waitress. I'm sure all that would convince her.
I checked the original LN and our current arc lines up with the final volume of that, so I'd say this will likely be the final volume of the manga.
It's not an Axe though, it seems to be the planned conclusion of the story.