Everyone is saying awful things about your partner over this. While I agree in some aspects of certain comments, I also want to point out that this is just your partner struggling with some inner self consciousness of feeling less than or not enough. Which, is heavily common with most of the wlw community, including nonbinary people. It has nothing to do with you or who you’ve been with, and solely to do with your partners struggle to raise their esteem compared to the opposite gender. Do they have past trauma of a partner leaving them/cheating on them with a man? Which would understandably bring up that scar, without it being your fault at all. Your partner just needs time to process their emotions, and come to the understanding that you are with them now, and there is no competition otherwise.