She feels I've given her an ultimatum - accept this, or divorce. (...) I've made no such ultimatum,
Hmm, it seems to me that you have. "This is who I am and it is no longer possible for me to ignore it" is pretty much the same as "I have come to accept this, and now you must too." If she truly can't accept it then separation seems inevitable. But my gut says you'll stay together.

Shock, then anger, perfectly natural. The five stages of grief apply here too. Next comes bargaining, or has that already begun?

I can't tell you how much I admire your courage.