Let Azunyan be poly.
(Really, though, there's no real indication that Azusa's plans are sexy plans, and she's certainly not sneaking around; if Jun's objecting, it's very passively. My read on the situation, which may or may not be warranted, is that Azusa and Jun's relationship is kind of casual, and that Azusa is still pining after Yui in a in-denial way, and that Yui, as always, loves her kohai but hasn't given an indication that she wants to take the relationship farther than her frequent hugs.)