The most annoying thing for me is that the whole drama is 100% in Shiho's head. She never managed to interact with Aki in a romantic manner, and neither Aki did with Yori, yet she already created the whole narrative on her own and now she is "ending it" on her own too.
Aki is just living her life, moving on from her own heartbreak, not being toxic to anyone, and Shiho is in the corner, being all moody, overdramatic, trying to... I don't know... stick it to Aki? Or Yori? Meanwhile, Yori is also completely unaware...
I have to agree with the statement that she wandered in from a different manga. She feels like an overdramatic emo kid surrounded by a bunch of peppy cheerleaders.