It's not just you, hon. *hug*
The thing is, now she knows, it's not something you can just 'put back in the box', as it were, or pretend it doesn't exist anymore. Say for a second you did go back to trying to live as a man. Firstly, do you think that would get her back? Secondly, how do you think she would feel knowing what you were giving up for her? If it were me in her place, I wouldn't be able to live with knowing that someone I loved was not being true to themselves for my sake. That would be just too selfish for me to deal with.
There's a saying, hon. If you can't love yourself, how can you love anyone else? How you think your relationship with your ex would be, assuming you did get back together, when there's an elephant in the room that both of you try to avoid even thinking about, much less talking about? If you're busy thinking about the way you're feeling, and how miserable living as a man makes you, how much of yourself can you give to her, to concentrate on how she's feeling and her needs?
You can't blame yourself for wanting to be yourself, hon. It's a basic human need to be able to live as themselves. It's not as though you had a choice about the way you feel. The whole point of transition is to enable you to live your life with your perspective focused on the world around you, and those you care about. Rather than internally, at war with yourself, leaving no room for thoughts of anything, or anyone else. To be able to be. To free you from this internal conflict and enable you to actually live your life. both the good and the bad of it.
I'm sorry that your ex is struggling with it, hon. Really I am. And that you feel the way you do, too. Sometimes things just weren't meant to be, especially if you have to live a lie in order to facilitate it. Relationships are about truth, honesty, about being yourself, sharing your heart, and having that reciprocated from the one you love. You can't do that if you're already lying to yourself, much less the rest of the world.
*big hug*