So, I can kinda see what the author was going for here, basically making the girl be ultra sadistic to the point that she expressly takes personal joy out of seeing the person she cares about suffer, while conversely also wanting the person she cares about to be happy which created a bit of a conflict for her, from that perspective I appreciate that she didn't just have a change of heart now that she sees he's found someone who doesn't need him to suffer for their relationship to work, as if she gave up now it'd just raise the question of why she didn't at least tone down her sadistic impulses enough to not cause him trauma, as well it'd help explain why she focused on bullying him to such an extent in the past and would follow him to bring her back into the story. I however take personal issue with the execution of her character, setting aside how we didn't get a great reason for why the group of delinquents who regularly beat people up didn't just kick the shit out of her when she has no real fighting ability and was actively antagonizing them, I feel this didn't really explore the guy's trauma well.
See, I'm not saying he needed to be tormented for it forever or anything, but it was clearly set up as a very deep-seated issue that was one of the major barriers to him realizing that he wasn't being bullied by his now crush, as he had been basically conditioned to think that people want to bully him, he did try to stand up to his bully and overcome his fears due to his growing affection and wanting to protect someone who he cared about but that and finding out, "Oh but I actually love you so it's funny!" (note, while we're going to see her continue to bully him without serious repercussions, this will be done for the sake of humor taking advantage of how it's a comedy, her bullying is very clearly portrayed as wrong) that is looking to be the 'resolution to his trauma for the most part, which I feel isn't quite enough. The sort of trauma that he was showing earlier on in the series seemed to be on a higher level than simple fear or apprehension, which is what this arc has basically boiled it down to... Might just be me, but I was hoping for something more akin to there are various times that he's being bullied that his trauma clearly causes him to act in ways that he doesn't want to (goes along with what she says, paralyzed by fear to stop something, etc.) with him having to clearly fight against a moment and overcome it later on because she crossed a line, here we saw him recoil in fear to her a few times but he basically 'stood up' to her right from the start with the deal and that's the end of his arc, now we're just brushing away the fallout from the past under the rug by humanizing the abuser, taking attention away from the victim...
TL;DR- While I get what they were going for with the girl, I think that this arc was kinda rushed and took too much focus away from the guy dealing with his trauma, to an extent that trauma comes off as a lot weaker in this arc than it had previously.
