Here is an update to the hypothetical situation, somewhat changed from the original scenario, as there has been much discussion between the couple.
Hypothetically speaking, what would you most likely do as a MTF transitioning for quite a while and you now find yourself in a nice relationship with another woman, it is lasting, it is getting serious, and she appears to be very supportive of you, BUT she says she insists on yourself remaining a biological male, legally and otherwise, to have a "normal appearing couple relationship" if you two get married because it would make things go smoother with her family and some of her friends?
Yes, you can express your femininity at home, vacation, you can continue to work as a female, be female in public in most situations, but for members of her family and some others potentially, to have them believe you are male. A male and female hetero couple.
While different to some extent, with more consideration given to her (the MTF's) female transitioning, this still a challenging situation for some MTFs. However, things could be worse. There is good and bad in this situation.
Chrissy