The answer you sick is very simple yes they do exist do you know? according to the series naruto doesn't have family so is sasuke so it is right for them to look at themselves as family since they have none. Coming to the real world this kind of friendship is common to orphans either at the home for the homeless (orphanage ) or if both meet some where in times of difficulties, as times go on they will come to soooo understand each other,care for each other and eventually, they will consider each other family since they have none