Yeah I definitely relate to all of this. Literally every point you make.
Some things that make me feel better, even though it’s not excusing anything:
She probably does feel safe around you and performative around other people. It sucks because she’s seemingly giving the best of herself to others and leaving you whatever energy she has leftover, but she probably doesn’t think she’s giving them the best of her. She probably thinks she’s being fake around them and it probably gives her anxiety, and she feels safer around you since she doesn’t have to put on an act.
Healthy communication that avoids blame is always the best scenario. Use “I feel” statements instead of “you always” comments, etc.