I think you're wrong about the part of her doesn't remembering, in the Mizora scene she says that even with the little she can remember, she can tell us stories. So, I wouldn't say she doesn't remember. It sounds, if anything, that she got lots of sexual experience.
But to be fair, I'm saying this from the top of my head, and don't got time rn to double check that scene. I may be wrong.
I meant that is 1 of the 3 things : 1.) It was encouraged in her cult, however she doesnt show any interest in anyone except your character and Halsin(Again thats why post was created). 2.) She doesnt want to show she is hurt by you cheating, considering her previous actions and her general attitude in that scene this could be the case. 3.) Bad writing All 3 is tolerable and fine things(except for Halsin of course) to me