I have been around a few people at various points in their journey and watched several specials on true stories of transitioning and come away with a not so surprising conclusion.
In most cases when a cisgender male who is married to a cisgender female comes out to her where she is accepting until he sets an hard date for gender reassignment surgery 99 percent get the eye's wide open thing going on, "he is really going to do it", "No more cisgender sex", "Wait a minute, I did not sign on for this".
Seems when the penis goes so do many spouses.
Now I don't believe it's just the penis as many married couples have less sexual encounters over the years it's now knowing conventional love making is out the door and the strong man they married is no more which comes from society drilling this into us from day one.
Can you truly blame the partner for wanting "out" of the relationship?
In the minds of many non-traditionals (non-cisgender) we don't see things the same way the significant other sees things and I believe for some this can change.
I would love to hear what others think on this topic.