spoiler
Butcher offers to start a new life with Ryan and is rejected. Then he sees his dog Terror has died. Butcher then takes the Kill-All-Supes virus to Vaught Tower intending to release it. Hughie finds Terror has passed and realizing Butcher's intentions heads to Vaught Tower to stop him where they have a fist fight that ends in Hughie shooting Butcher
It's a solid ending for the Butcher character and was obviously needed to wrap up the story. The show was about more than Homelander.