Hi Garlicmaster.
I have been absolutely NC with my entire FOO for over six years now. It was sort of me that initiated it, as a cry for help, but they embraced it fully.
I understand fully your sense of guilt - I felt that for so long. But, as I heal a little, I am seeing that I have no reason to feel guilty. I can see now that it was the only healthy thing to do, for all of us. Every interaction was so distressing for me and my family. Possibly this was the case for my parents as well, but it's hard to say for sure, because their psychological defences are so strong, namely, they are perfect and I am awful!
The relationship had nowhere to go, especially as I set about trying to heal a little.
In terms of life events, your partner's transition is much bigger than my daughter's decision to co-habit, but I remember feeling so relieved that we were NC because they would have been so difficult and unpleasant and would, I am sure, have tried to stir up difficulties between me and my daughter. They are very definite in their views, to say the least! She has just split with her boyfriend after several years, and I can imagine what they would be saying, all along the lines of "we told you so" and a lot more besides.
These "toxic" or "difficult" parents can't change. They have no will or reason to change. Only you know what is right for you but whatever decision you make, it is the right decision for you, so don't feel guilty.
Best wishes to you and take care.
Libby.