I'm not worried about Haruki, personally. The author hasn't given any hints that Aya is interested in her at all. If anything, Aya seems to be trying to separate herself to some extent and often reacts with outright hostility if Haruki tries to get too close to her.
Honestly the only two endings I see at this point are Aya and Sei getting together or everybody ending up alone and relatively miserable. The latter is what I consider much more realistic than Aya ending up with Haruki.
The last page's text seems to be a foreshadowing that Aya's friendship with Haruki gets obliterated after this anyway. I bet she forces Aya to look at her feelings for the two of them, and Haruki loses out to Sei.
Also, in case people missed the subtext, Aya's interest in the skirt length and willingness to try it is part of an effort to be Sei's "Yoru" by being more of her opposite. She seems to discard the idea at the end, which is probably for the best.