I don't know whether I can believe Tobio or not. Like, maybe he's all okay now and buried everything after his suicide attempt, but I don't really feel that way. It's like he's just shutting it all down with being super outgoing, loud, happy go lucky person.
When he was falling, he thought that could be his atonement. What if he's trying to atone right now too? Like, befriending his bully, matching him with Renko, being a good son and brother... and then trying to die again? That's just a thought though.
Maybe he's just trying to give up on Renko, because she knows about the incident and that he was a part of it. Minami doesn't know anything about him aside from what he showed her, so maybe he's trying to get as far away from his reality as he can?