I'm sorry. This sounds so hard. You have the advantage of advance warning/planning time, though, so that's good. Do you have people to support you if her reaction is ugly? A place to stay, a therapist, etc.? As for getting sucked back in... .you mention sucked back into the situation you've been living with (double life), and that seems like a no-go. What if she turned out to be (or said she was) willing to love you as a woman? Her psychological problems would seem to be a harder situation to draw a line on.
But I guess you'll cross that bridge when it crumbles or something. Anyhow, courage!
thanks for the reply, Steelwork! yes, I have many people who love and support me. Including a couple of polyamorous girlfriends. Yes, I know, I should not have gone there while still married, but it happened and in some ways, the love of my new partners is making it possible for me to move forward.
We tried dealing with it years ago and she did not seem at all willing to deal with it supportively. She invalidated my female gender identity. She said some very insulting and hurtful things, including using the word "nauseating" to describe how she feels about me becoming a woman. I found a couples therapist for us, she quit. I found support groups for spouses of transgender people, she quit those as well.
Even if she does now say that she is willing to accept me as a woman, I am not sure I will truly believe her, or feel comfortable with her. If nothing else, the word "nauseating" will be very difficult to get out of my head.