https://collider.com/the-office-brian-boom-guy-pam/

Nobody was asking for this Season 9 twist.

People hated Brian because he was a slick talking snake trying to breakup a solid relationship simply going thru an argument. The argument wasnt even severe. Nobody yelled or called the other nasty names. Brian didnt care how many people he hurt. He only cared about himself.
Unfortunately, snakes like Brian (and Cathy) are all too real in life.