The point of no return for me probably came when I started getting consistently gendered correctly, only about 2 months ago.
In hindsight though, I think from the moment I began therapy in earnest I was already too far gone to consider turning back, even if I balked at moving forward sometimes.
I can't go back to living as a man now. I would rather undergo some kind of barbaric execution, like being devoured by lions or burned at the stake, than to try to be male again.