Like others have said, the MC shouldn't have such a trauma from that single incident of betrayal. He has underlying mental health issues, so he merely incorrectly attributes those panic attacks to the incident with the nasty girl, not knowing any better. If you consider how he could reshape himself with such dedication, in such a short time, for his high school debut and then carry on to get friends normally, it's quite obvious he's not a person totally broken by bullying. Yet he gets those dramatically debilitating panic attacks. He needs to see a professional to figure out what's going on.