Rooting for nanao. At this point in the story it wouldn't make sense for Asumi to be romantically interested in Mai, at least not to the degree that she is towards Nanao. Poly is great, but at the moment I don't see it.
When Asumi does meet Mai again, I imagine that Asumi and Mai will sort out their feelings (rather than having sex), given that the vibe I get from chapter 1 is that Asumi just wants closure and make up with Mai. I wouldn't mind for Mai ending up being an older sister figure.