Who is "him"? If you are talking about that kid from your high school, then it should be noted that having a crush isn't the same as establishing a parasocial relationship with someone. A crush is just you feeling attracted to someone. A parasocial relationship is having a one-sided relationship with someone. Think of it like comparing someone who happens to think that their teacher is kind of cute vs someone who is an extreme swifty (the ones who refer to her as "mother").
Along with that, the situations are completely different. You are talking about a high school, where things like social conformity/peer acceptance will also play a role in how students treat each other. A lot of school environments tend to have a social hierarchy and a lot of students try to maintain their place in it or climb up it by trying to follow what others are doing. By comparison, with celebrities, the relationship is typically one-sided and there isn't usually as much social pressure to ditch the celebrity if they've done anything wrong, especially since there is a good chance that people will forget about it and move on once the next big thing happens.
Along with that, a lot of fans typically tend to hang out with one another, whether that be online or in real life. Fans usually tend to have their own little communities/in-groups that revolve around their favourite celebrity. People tend to like being liked, so in order to be accepted by others in our community we may conform to the group "rules". Over time, being a part of these communities can lead to things, such as group polarization. These communities may produce a disproportionate number of arguments in favour of a cause in relation to whichever celebrity the community revolves around that they already support to some extent. People may also adjust their position to the most dominant one to be better liked by the group. Over time, this can lead to these communities becoming increasingly extreme. This mixed in with the fact that celebrities make money off of the parasocial relationships they harbour with their fans, encouraging them and their management to further feed into them, likely results in an entire community of people who are willing to defend these celebrities with every fibre in their bodies.