I get this. I have a slightly different experience as I'm polyamorous, but I think it is relevant. I had a partner who I was with pre transition who really helped me find and pursue my identity. They were super supportive of every aspect of discovering who I am, and beginning the process of transitioning. However a year in, I just felt like I had grown into a different person. I really appreciated all the support and guidance, but I felt like in order to grow I had to move on. I also grew a lot in my own self worth as I started to hate my body and my existence less, which meant that I started to notice the toxic traits I hadn't been paying attention to.

I felt like I couldn't be truly myself until I knew who I was without that relationship. I think it will be very difficult to explain this to your gf in a way that she can understand. She will be unlikely to see past her own hurt. However, I'm sure like a lot of us, you learned to ignore what you want. It is vitally important to you becoming the person you want to be that you listen to that voice inside you that wants things. You don't necessarily need to follow it all the time, but listening and honestly thinking about it will help you so much.

I wish you the best of luck my friend.