Does the main character live her life just over reacting to things? That's really annoying. Story is meh and characters are flat.
I've never really been let down by an idol, heck I've never even had any, but if I had one and looked up to them (like the way Ito looked up to Sumika, which was a lot) for being known as a popular, sweet, caring person, and it turns out they were even the slightest bit the opposite, I'm sure I'd be upset.
Also, we get a one-panel sized flashback, if I'm going to make assumptions here, it seems like Ito looked up to that girl in the panel but she probably turned out to be a rotten person, possibly even worse than Sumika, which maybe caused Ito's sensitivity to fake personalities.
If I had to choose a real life example (even though I know this won't be of the same degree as this story, since this is a far-far worse situation) but let's look at Michael Jackson. He was accused of molestation and people today are still arguing over this, over a decade after his death. I know my parents still have doubts about believing the allegations because he was such a big pop star, who touched many people's ears and hearts.
If she's already experienced being let down by the reality of a person she put on a pedestal that makes her less sympathetic because she's still putting people on pedestals and has apparently learned jack shit from that experience. The only sympathetic excuse for this behaviour is naivete otherwise it's just entitlement.