@octopuslines it's mainly because I had some bad experiences in the past, luckily not as extreme as Junu's, so I can easily relate with how he feels, but I feel his sudden outburst is...too sudden, given that just a while ago he seemed content (or better: resigned) with his role. Of course in between he saw the girl he likes completely rejecting his real self and he thinks she got together with the rep, so even his last bit of hope of being reciprocated is shattered and that hits really hard, so I was expecting a huge change in his personality and attitude, but not in this direction.
Or maybe...he simply isn't as much as a good guy as I thought.