What are the "common-law" marriage laws in your state? Your partner might be covered if the common-law marriage laws in your state recognize the two of you as being married even though you have not gone through the motions of getting married. If you are, in fact, considered "married" in your state by virtue of common-law marriage, that could be why the "domestic partner" language doesn't apply to you.

Or I could be full of beans. (Or both.)