Jewish Not Being A Race.

My step father is Jewish. I, as well as the rest of my family, believe it's a nationality. I mean they can get a disease no one else can. Yesterday at thanksgiving dinner my fiancé said something about how it wasn't. Today I confronted him about it. He screamed at me until I was in tears. He says the US census doesn't say that it is so it must be that way. I'm really hurt. What should I do?