I think it was vague enough. Don't overthink it.
So now I am faced with a dilemma. How do I answer this question in a way that a.) is honest (NOT lying to children is very important in my family) and b.) won't contradict any explanation for Dude's presence that my sister may provide to my nephew? What is a seven year old's concept of "husband" anyway?
If it comes up again, could say: "I am married to Mr S. I am not married to Dude. But we're roomies and all best friends." There. Legally married means one legal husband right now. It is honest and age appropriate, and if REPEATED by the child to someone else doesn't stir hooha anywhere that would come back on you.
A kid that age can have a concept of a "husband" and a "best friend" -- so its not using big words they don't have a handle on.
Since you are not "out" to your family and don't seem to be inclined to go there at this time, that could work "good enough for now" and when things change as the kid grows, you can adjust your responses then.
And for entertaining conversation, could ask the kid "Well, what do you think a husband is? What should a husband be able to do around the house?" just to know where his little brain is at at this age.
Or go safe with other conversation paths:
- "Do you think one day you might get married? Would you have a big wedding cake or a small one? "
- "Do you think one day you would have a roommate? Would you live in the city or the country?"
- "Do you have good friends this year in school? Are they totally new or old friends from last year's class?"
Early elementary school is still very self centered -- they want your attention as THEIR audience so they can yammer at you about THEIR stuff. It's not so much about you too much.