Alright, this is interesting.
Hebikawa does have that bad personality trait of needing to know everything and be in control of her surroundings, so I don't blame him for suspecting she would something bad to him if she knew about his secrets. She did go out of her way to ascertain dominance on Kusunoki with her sudden calling of her friends and the times she pursued the protagonist after seeing he was visibly sick with her mere presence, disregarding his state. I do not blame him for thinking she was plotting against them.
On the other hand, the things that he were most conscious about were things that mattered to him and no one else. He is a teenager with image and self esteem problems being faced, for the first time, with the reality that people do not put the same value on his image as he does. I know there is a name for this type of thing, it's called Phantom Audience if I'm not mistaken - it's a type of fear that makes you believe people are watching and judging your every move at all times, and this seems to be what our protagonist suffers from.
Is this story about a boy with image issues coming to learn that the world doesn't care about his traumas, or is this a story about Hebikawa being an evil manipulator who wants him to believe she's not his enemy so she can strike from his blind spots where he can't even understand that he's being attacked? Or perhaps a mix of both?