I think its a choice a lot of artist that make yandere/stalker stories have to do. The whole point is to have a character that has an unhealthy obsession with mc but if its not an one shot story, what do you do with the characters after the main scene with the revelation of the stalker? Do you validate and give favor to him bc he's the male lead or do you try to give him a redemption arc where he unlearns and pays for his behavior?
The creator is choosing yamato rn and is keeping the world of the story so small, like the cast os characters being only shown when they're thinking or talking to Rin, so that yamato feels like he belongs there just the way he is. I feel like a lot of his actions are being excused bc yamato has "true feelings" but is mostly bc he's the chosen male lead and im sure that the creator thinks he's more interesting in this form without stripping him completely from his creep behavior (and even making the second male lead assault rin was like???? Ok makes NO sense for this character personality but i see your intentions)
The pink haired prince disappeared out of thin air