Main Squeeze is definitely a possibility.
I don't know about archduchess, tsarstepan."Lady" is a term that Dys came up with. He knows darn well that I don't fit the description most of the time.
What I do say most often is that, "We are living in sin and loving it."
When dealing with people who might give me a hard time, I might say partner.
In fact, I do consider Dys my husband. I feel more married to him than I ever did with my ex whats iz name.
Mr. Dys, you know that I love you more than life itself, that I w0uld do anything for you and that my life began when I was sixty, when we met.
I guess what I'm trying to say is, "Snap out of it, Sweet Cheeks!" Whatever I happen to call you doesn't ever change the way I feel about you.
But I will not call you "my partner" again. If we decide on more royal names, tell me if you like "Archie."
or, we could go with Old Fart, Blue Eyes, Cowboy, Grumpy, My Love, My Sweet, Sweet Man, The Love of My Life, or simply, Love.