Is a tag question, one part positive one part negative. 'You hate vegetables, don't you?'

First, put a comma there. Also, it looks more like a question. "You are my friend, aren't you?" If you put "aren't you" in a sentence, you're just making sure he's your friend. I guess in Spanish, it's the same as "Usted es mi amigo, no?"

"You are my friend." - This is a statement. "Are you my friend?" - this is a basic question. You are asking for information. "You are my friend, aren't you?" - this is called a 'tag question'. Basically, it means "I think you are my friend; tell me if I'm wrong." This is a question which asks for confirmation, because the speaker already has an opinion (You are my friend). The negative tag of "aren't you" is used to provoke a positive response... hopefully. The question "Aren't you my friend?" works the same way.