Hi Shauna,
I see you've been struggling with this for a long time, so this is an excellent step.
If the psychiatrist is truly professional, and you have every right to expect them to be, you need to be completely honest with them or they won't be able to properly help you. They are trained to be non-judgmental and have seen it all before. They're pretty good at detecting when you're hiding something, so you're only hurting yourself if you try to play games and outthink someone who's had years of specialized training.
I experienced something like your fear when I came out to my primary care doctor. I just finally decided to demand professionalism from him, and he came through.
I was fine, and you will be, too. Just lay it out and let them do their job.
Stephanie