I can’t say, because it all depends on what I was expecting from the relationship. For example, if I was expecting children, that would be a problem. I’m not prepared to say what I would do. All I know is that it turned out I couldn’t have children the natural way, and I would not have blamed my wife a bit if she left me to find someone who could give her children. She chose to stay with me. Probably an instance of loyalty over wisdom, but it worked out for me.
If it turned out that the woman I loved was a man, I would be disappointed for sure. But then, maybe it wouldn’t have mattered because neither of us could have children the normal way. So we might decide to adopt. Or, I might have wanted to find a way to have genetic children. But maybe she would have let us use a donor egg and gestational mom.
Then again, maybe it wouldn’t work out.
And I’m sure there are a host of other expectations people have that would be impacted by this unexpected bit of knowledge. I carry the genes for cystic fibrosis and mental illness. Would my partner leave me when they found this out… when I found out? It’s happened before. Many, many people won’t stay with someone if they are mentally ill.
So I don’t trust glib answers here. There are too many implications that we cannot anticipate. People may work through them or not. It’s really not much different from any other relationship where both are genders they believe themselves to be. You see what happens as you go along. But if you love someone, you usually make a big effort to work it through. One big thing is generally not enough to knock you apart.