Twin who's afraid to come out

I'm drab and a twin. My sister is hugely supportive of anything LGBTQ and I love her for that. In my head, I know she'll support me when I come out to her. But I don't want this twin bond thing to go away, because we lack this one thing. I'm scared it'll be too tough for her to accept that her twin sister, whom she's been steadily growing closer to over the years, isn't actually that at all.