Rock opera is definitely the first straw that broke their relationship.

Then I think he started making things official when Bojack left to go to Michigan and he spent that whole year without any Bojack in his life, which he admits to being a good thing for him.

The whole Oscar thing and finding out that Bojack slept with Emily was probably the final one. After that point he had officially stopped living with Bojack and stopped being his punching bag for when everybody else didn’t wanna indulge him.