Feel like we're missing a major piece of information here, like the ex-GF is deaf and dumb or clinically brain dead. Or so autistic that she cannot recognize basic human forms.

Alas, probably just a fanfic. OP wants there to be a world in which she passes so well that she "had a cis girlfriend for 9 months, but uh, she like, had to leave, but she was totes real dood"