I speedread this in 2 days. I honestly evaded the series when it just started because I wasn't sure if it was queerbait, but I'm happy to see it delivers. That said, I found the last arc a bit weird? Not that it would be unrealistic for Aya to get jealous like that, but the way they behaved around each other seemed a bit random more than anything. Other than that a very nice read.
Jealous? Aya didn't really get that jealous in this last arc. That was where we all thought it was going to go when the arc started and the underclassman started going after Koga, but that was a misdirect. UC was actually just interested in Mizuki's music, and Aya recognized the opportunity she presented for what it was and tried to push her to take advantage of it, even though she really, desperately wanted to ask her to prom.
Now that we know for sure that her feelings for Mitsuki were romantic in nature, it does make that part a bit more ambiguous in retrospect IMO. The MAIN thing was obviously the potential career thing, but there might have been a bit of jealousy underneath as well that Mitsuki was getting close to another girl and she didn't like that .