Noriko's also had a lifetime of coping with the fact that Niki will never let Akira go completely, so the best Noriko can ever get is a share, and by the time she enters the events in the story, she's already had years to come to terms with that.
Ayane has none of that. Her entire experience with Akira prior to the school year is that Akira has three girls in his life outside of the classroom, his neice, who of course will never be a romantic rival, Maya, who appears to not want to be one, and Ayane. So Ayane is able to build this fantasy that she is the only one for him, only for it to be shattered once things start to develop in actuality, and Kirin forces her way into the bedroom, and she finds out about his present relationship with Ami and past relationship with Maya, etc. She's had no time to process this, we're literally watching that process play out in real time.
She also has the added baggage of a fear of abandonment. Her mother walked out on her, her father began ignoring her, and now she has to compete with literally every girl and woman with a face for affection from the man she's convinced herself she's fallen in love with. It's not just that Ayane and Akira's relationship isn't healthy, it's that Ayane can't have a healthy relationship at all right now. She needs a therapist, not a boyfriend.