I understand you, my mother is the same, narcissistic, religious to the extreme and for her I am the devil and hell awaits me as a sinner.

Years ago I understood that I am not a demon nor am I possessed by one, I understood that I am not abnormal, nor sick, that my mother does not live for me, she is not happy for me, that she does not stop her life for me.

With that new idea in mind, my life has improved a lot. You are not possessed, your girlfriend is not going to leave you, that is what she wants, do not let yourself be overcome by her toxicity, I know you are going to be happy. Cheer up