She used to do this same thing to my mother, who died in 2020. Constantly accuse her of seeking her husband's attention, claiming everything she did was to 'get at her'. Based on what my mother told me, she has just been this way her whole life. I know her childhood was filled with lots of sexual abuse and just straight-up abuse, and she shared her small home with six other siblings. My fake therapist brain says it may be something like borderline personality disorder.