I guess we are supposed to believe that, in leaving his father, Iori becomes aware of his worth as a person and not a stressball unto which frustrations are released,,, but he goes right back to Manabu who'd done just that - and drove him away right after no less - on some cheap promise of "doing better."
I suppose it's fine if you look at the ending as being bitter sweet, with Iori leaving one broken man for another, but I just don't think that was the intent. Just feel like its begging to be taken seriously as a Mature manga.
Ballad of Back Alley