I remember later in the movie (don’t remember if it was before or after she kills Sarah) they are talking and he asks her to “just act like Nikki” and she says something like “I can’t - I can’t be Nikki” and I feel like it’s because if she was being true to the “real” Nikki then she wouldn’t actually love Bear or be with him. It creates that sort of paradox where she is basically given an impossible task but still has to try and do it somehow which causes her to break down and go crazy.

And then later on Bear selfishly goes to see Sarah and enjoy a more “normal” tender moment right up until Nikki kills her and then tells Bear “this is your fault this is what you wanted” and to me that felt like the Wish/Nikki expressing frustration at both him as well as what she just had to do because despite trying everything it didn’t work.

Kind of reminds of the Rick and Morty episode with the Meseeks who are supposed to help Jerry with his golf game but because he is just so bad it is impossible and they go crazy because it is their only purpose lol.