So about a month ago my stepmom started refusing to let my dad see her phone, was leaving the house way more often than she ever did, and straight up just treating my dad like complete trash; yelling at him for nothing, not being thankful for him cooking dinner, not even sleeping in the same bed as him. 

He's been understandably torn up and angry about it, and confided in me about it all. Since then I've ignored her texts, Facebook posts she tags me in, everything. 

Today is my birthday and I didn't respond to her birthday wish to me and she angrily texted me asking why the hell I'm ignoring her all the time. I have no intention to talk to her, because if I do, I won't be saying anything nice. Am I the asshole?