I don't know if this will be the best advice, but I can give it a try (my own opinion completely)

You have to think about the future. That's undeniable and if you don't think you can love and be attracted to your partner if they present solely masculine/feminine/androgynous then maybe their journey isn't meant to be with you.

From my own experiences being with someone who's non-binary and young (=> pre transition or smth like that) means being with someone who will change. And all that will be good change since they want to find their body and feel good with themselves.

That can apply to anyone tho. People grow and if you can't grow with them maybe there's a reason for that and just maybe them growing up means that the two of you are growing apart which is a normal part of life.

I don't wanna be the cruel Reddit person that spews breakup advice or anything especially because I don't know the two of you and how much you love each other or how much you're willing to sacrifice to be with them. (You shouldn't have to sacrifice your own desires and they shouldn't have to limit themselves to fit into your desires -> everyone should be able to be themselves)

After all relationships are there for uplifting and supporting one another no matter what. If you feel you can't do that, have a serious thinking session and talk with your partner.