Maybe my experience will help a little. When I first met my best friend Stephanie, in 1981, I (who am classified as "straight") didn't know she was transsexual. We became friends and I realized there was something different about her, so one day I just asked her. We sat down in a coffee shop and she told me how she'd been born a boy, but knew she wasn't really a boy, and how she eventually had surgery in her early 20s, I think it was. She told me the whole story. I was a bit taken aback at first, but it didn't take me too long to get used to the idea.
Then, after that, we never talked about it again until recently. Some years ago, she became a Buddhist, and she says this helped her to accept herself more completely ... both her masculine and feminine side, and now she is much more comfortable with herself (this makes sense to me because I don't believe anyone is 100% male or female). So we talked about that for a bit, and that was that.
I guess what I'm saying here is that all those years when we didn't talk about it any more were just fine with me, and with her, too. Really, there wasn't anything to talk about any more. I think this may apply to your situation, too.