Sachi said it herself, if Punpun REALLY wanted to find Aiko, he wouldn't have chosen such a retarded way of trying to meet her again. All he was doing was running away from his future.
Sounds sensible enough to me. I mean, if you lost something in your past, what's the point of searching for it in the future?
Thinking back, I almost want to look back through the volumes and see if Punpun has ever
made a decision of his own volition. I mean, the reason he is where he is in life is because everyone else kinda pushed him there, for one reason or another. In the few times that he was left to his own devices, he usually ended up holing himself up in his room or something. The only time he has ever gotten close to exerting his own individuality was (ironically) with Takashi, but it seems like Aiko's return pretty much killed him off for good. So in a way I can't really blame him for what's going on, any more than I can blame the leaves for landing in my gutters.
It almost reminds me of Watashi, in a way. Both protagonists were essentially driven by their surroundings, and both stories leave you wondering what would've happened had he actively acted
within their situations. The only difference is that Watashi got to have do-overs, but Punpun has to live with the consequences of his inactions until he breathes his last.