How can I tell what I am to a guy?

I don’t know what I am to this guy. I’ve known him for 8 months and around the 6th month I asked him what are we. I was introducing him to my sister and I told him to introduce himself. He said he wanted me to introduce him and to tell her what we were. I didn’t know what we are so I asked him but he wanted me to answer. But I have no clue and he wants me to give the answer.
How can I tell what I am to a guy?
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