Whew, yeah this is a tough one.
Hyouka liked MC throughout their childhood, but MC only sees her as a friend. MC was never romantically interested in her and to confess to another girl.
First, Iori;
On the account that he was a middle schooler then, I'll give the naivety a pass, but his ignorance to why Hyouka treats him the way she does is unpalatable;
1. She changed her tune to him alone.
2. She knows about the confession, meaning he should've at least realized that she knew "he ditched his friend he knew since childhood for some class flower who was just being nice."
Onto Hyouka...
1. Why is she so fixated on Iori? I can't think of a single reason why she would actively interact and attack a guy who, not only doesn't reciprocate her feelings, but doesn't respect their friendships on the same level as herself. The only justification I can think of is that she wants to tear down his self-esteem while remaining close to him. He already stated that he doesn't have friends so maybe she wants to make him socially dependent on her? I don't know, but that idea sounds worst. Just move on. To facilitate it, stop interacting with his family. Cut all ties, else you'll continue to cling. If not, be honest for once and fucking confess. His dumbass has proven to have the social IQ of a toddler, so unless she makes the first move, he'll find the next "nice" girl to cling to.
Lastly, new girl...
1. I don't think she is the girl he confessed to. MC's like Iori are only perceptive when it comes to appearances so I believe he'd recognize her, but assuming she IS, what reason does she have to interact with someone she rejected? Maybe as a social butterfly, she was being nice to him to boost her image in middle school. But now, maybe she could be using him to help boost her image again, since as a transfer, it'd probably be easier to do so through a known connection... But he's in a different class, so even that is questionable. If she, for some reason, DO like him, why reject him? Did she like him before or after the rejection? If it was after, what about him changed that she liked? What about her changed that could've influenced her interest in him?
If it was before... I don't even want to dig into that.
2. Assuming she isn't that girl, which is what I think is the case, I have nothing to really say about her as a character... that's a lie, what the hell was that at the end? Did him coping a feel flip something in her? Why did she latch onto him so soon and abruptly? From her reception to getting felt, to her touchiness with Iori, I'm going to guess this has to do with her old school and her being a transfer student.
Am I interested? Interested enough to write this, but will I invest anymore time and thought into this? My senses are warning me, and I've learned not to go against them when it comes to media catered to the "new youth." I doubt this will be a fun read, so I'll have to pass.