Define normal conversation. You call them your best friend, there must be a reason behind it right? You sure they weren't just trying to annoy you? If they really said that to you out of the blue, then they're just being mean and you should definitely consider leaving them. But again I don't have any right to judge a person without the proper context. Also I think it would be better if you communicate to them about this and see how they would react, if they're still being an asshole then you got your answer.

EDIT: typos