Many folks, including yourself growing up, were probably told to believe whole-heartedly in the gender binary. The binary told you where to go with your life, how to act, it chose your direction like fate or a destiny I never asked for. But as humans, we are not a computer binary of 0 or 1, but a spectrum of multiple possibilities, or not on the spectrum at all, devoid of gender.
Our gender in this society is synonymous with our sex. However, as being nonbinary it is hard to see it that way. Having only two options as a nonbinary person is like in the matrix when you’re given two pills to choose, but this time it’s pink or blue, and both of them lead to horrible personal demise. You bring out some purple pills and say, “Sorry, I’m already prescribed!” but that was never an option. You can’t be your own doctor!
But surprise! Your gender doesn’t need a doctor’s diagnosis. Gender identity is who you identify as in society. It’s who you are and who you want others to see you as so that you are comfortable in your own skin. If I went up to a cis woman (someone who identifies with their assigned gender), and said to them, “You don’t look like a woman you have more of a man-looking body.” it would be extremely disrespectful. She would be confused and shocked and uncomfortable that I even mentioned the fact. Because she identifies with her assigned gender. And wants others to see her as such. And someone calling her a man makes her feel embarrassed and anxious.
To me, it feels that way whenever I am called ma’am, woman, girl, sweetie, lady, and any other term (and mildly sexist) pet names for the “female” gender. It makes me uncomfortable, it makes me feel like I want to jump out of my skin. And the feeling has built up over the years to become depression and anxiety-inducing, (no thanks to being in customer service).
I know that it is hard to rewire your brain like this. We are socialized in this society to think that there are only two. But the human experience is so much more. And just because we don’t have all of the terminologies exactly right yet, the feelings are there. And the experience as a Nonbinary person is as real as can be.