Please give me the strength to not send that happy birthday text

We've been broken up after 4 years together for just 2 months. She blindside broke things off, refused to put in the effort to fix us or go to couples therapy, and then started fucking a new man as a casual fwb not even 2 weeks after the breakup. I've been no contact for about a month after hearing about her fwb which she had and then ended shortly after starting it because I felt utterly betrayed and couldn't handle talking to her anymore once she was fully moved out and our things were exchanged.

Her birthday is in about a week and I'm seriously struggling especially after spending the holidays alone. She is obviously gone and did not appreciate me for the great and loving partner I was to her. But somehow I'm struggling to not send her that happy birthday. Even after all the betrayal and hurt she put me through.

Please just give me the support to stop thinking about her, accept we are done for good, and not send that dreaded text. Thank you for any and all support I just want to be able to accept we are over and try to think about her less.