Thing! The Thing happen! Sound the alarms!
And of course she still gets cockblocked in the end lmao
It's not ending too soon at least. This'll be the first chapter of vol 7, meaning at minimum we're getting 4 more chapters. It could go longer, of course. There's still lots of ground left to cover:
Asumi and Mai have to meet up again to reconnect, not through the brothel (also, Mai is in Tōkyō for work, and she probably can't just leave her assignment early, so that meeting could be a while.)
We still have to get a Mai sex scene cause there's no way this series is ending without that happening.
We still need to resolve Nanao's story. Presumably Mai will confess at some point, and that will put Asumi in the position of choosing between her and Nanao, which could also lead to poly.
(even in the event of only dating Mai, there's no way their relationship is gonna be fully closed and monogamous. Mai's probably not gonna wanna quit her job and even if she was ok with that, Asumi wouldn't want her to quit either, and Asumi is definitely not kicking that brothel habit, girlfriend be damned. She's an addict. You really think that's how this manga will end? "Well i used to love lesbian brothels but I'm over them now that I'm in an committed, exclusive, monogamous relationship!"? Come on now. This isn't that kind of story and you know it.)