The Boys missed the mark with adapting Butchers ending
Butcher is the single most cohesively written character in the whole show because at the end he really moved like someone who suffers from a massive Intracranial Tumor.
"My dog died a peaceful natural death, therefore all suppes must die"
Before you say "oh but that's not the point he realized he had no one left" - no, just no.
The key difference between the comic finale and the show finale is that in the comics Butcher killed him alone [or at least with Noir], in the show it was a group effort.
He was not alone, he accomplished his goal with his team, his people that deep down he is shown to care for - Ryan, Hughie and even MM at the very least.
Comic Butcher was not even as remotely close with The Boys emotionally bar Comic Hughie, he was portrayed as more sadistic and his story was narrowly driven around revenge.
Butchers and The Boys's dynamic is much more personal and familial compared to the comics that the ending does not make sense. He achieved his goal, he was not alone, not abandoned, not betrayed no nothing. Even in death he was forgiven, accepted and even mourned just as much as Frenchie whom the whole team loved unanimously.
It makes 0 sense that a character that has endured so much would be triggered by something like losing a pet in the best possible way. Home, old and in peace.