I think you've put into words the way I started to see things as the story kept unfolding in the last few chapters. This manga is very much about Naho's perception of himself and how others see him (or how he thinks other people see him) and we are only getting the perspective of someone who is most likely a very unreliable narrator because his world view has been so shaken.
People are dogpiling on Kana tbh when I think Kana treated Naho quite well. He checked in on Naho whenever Naho was acting strangely, but Naho was the one who ran away because he thought Kana would find him annoying.
Thank you so much for this It all makes sense now. The dots are now connected ヾ(☆▽☆)
Omg thank you so much !!!! It all makes sense now ヾ(❀╹◡╹)ﾉ~
From reading the translation
Kana liked Naho and always thought Naho was cute (notice how he smiled at Naho's bed hair) when walking together in chapter 2 (or 3, can't rmb).
In chapter 5, Kana explained that Aoi was moving away to college in Tokyo and he won't be seeing Aoi anymore, so Kana wanted to spend more time with Aoi to make up for it. That's why he's been studying with Aoi recently. Kana said that he and Naho would be together forever so he figured he should priortize Aoi for now as his time with Aoi is running out. Naho suggested that Kana should take a train to see Aoi on the weekend, but Kana said he didn't think it would be necessary. There was a part in the library where the translator thought that Kana was lying about studying with Aoi. That's not true. Naho was just thinking about how Kana was studying with another friend and not Aoi that time.
So no, Kana doesn't like Aoi.
Naho's insecurities were taking over and he misinterpreted Kana's friends' attitude towards him. The blondie actually thought Naho was cute, and took an interest in his origami. He kept asking Kana to give him Naho's origami but Kana refused to, so he stole the crane from Kana who got annoyed at his antics, which is why Naho saw the crane in the blondie's hand. We were MISLED into thinking that Kana gave the crane away. Aoi also found Naho cute, and treated Naho very nicely (gave him a candy).
Naho also started to interpret Kana's actions differently because he thought Kana found him annoying (his insecurities talking).
Kana knew that his friends found Naho cute, so he didn't want Naho to see them. That's why he got annoyed at Blondie when Blondie was all over Naho. Kana is possessive of Naho, which is not good tbh. I don't know if he wanted to isolate Naho. Right now all we know is that he's also jealous of Naho's new friends. He hasn't done anything to push them away from Naho yet, however.
In chapter 8, Naho asked Kana why Kana thought he was average. Kana said that he never thought that way. Kana didn't know that Naho overheard his conversation with his friends. He said that objectively, Naho's face is average, but it doesn't matter because to Kana, Naho is the cutest. I bet my money that Kana said Naho was average so that his friends thought the same way.