NC with my nMom is getting difficult

I left my toxic household nearly two years ago and live by myself with my boyfriend (I’m 21). I did not leave the house on good terms with my nMom. It’s been LC with her since I left, and November the 30th is when I last spoke to her.

My nMom was very abusive, emotionally and physically and is an alcoholic. Every time a major event came up, I felt so much guilt for not talking to her. On Xmas and new year I said nothing and I never wished her a happy birthday. Talking to her or even seeing her name pop up on my screen gives me anxiety and stress.

On Xmas day, she left me a voice note using my sisters phone (I have her blocked on WhatsApp) and she was crying saying she can’t believe I did not come home for Christmas. It ruined my whole Christmas and put me in a stressed and anxious state. All I felt was guilt, shame and sorry for her. On top of that, her brother had come to visit but I never knew because I’m NC with her now. This just made me feel more guilty.

Every important day that comes up stresses me out, because I know I may have to talk to her. And I know that I have to go through the day not talking to my own mother. Is this selfish of me?

Does anyone have any advice on how to deal with this guilt? I’m so happy here with my boyfriend and knowing she’s crying on days like Christmas makes me feel horrible. I know it’s probably not even real tears and just weird manipulation but I still feel guilty.