It hurts so badly to see someone you were close to change and become a completely different person.
Someone you respected and loved, even if not romantically but love them as a friend/family member/idol/whatever and to see them change from the person you knew, the person you liked and respected, to become someone you basically despised, someone you have no contact with, nothing to do with or in common with, is crushing.
It almost feels like a betrayal.
That may just be me being melodramatic as well, I tend to overreact about shit that doesn't phase other people, but for me personally it's a seriously shitty feeling.