Okay.
Aiko doesn't deserve yaguichi. She's just obsessive and unhealthy,and yaguichi is plainly a better person than her.
I don't know why punpun chose to say no. Is he trying to keep up a good person act? Is a he a coward that doesn't wanna leave? Or maybe he decided that what he was doing genuinely wasn't right.
Eitherway, aiko is gonna ruin yaguichi. Better choice romantically should've been accepting it by punpun and leaving,he's a coward fit for her, but obviously won't be healthy for either of them. Weird.