Followers have a one-way access to posts by the users they are following. Their posts will be added to your Friends timeline feed, but your information will not be displayed to your followed user.
Friends on Argus have full access to all of each other’s timeline posts. Tiles posted by your friends are viewable from the Friends tab, and your posts are likewise posted directly to their Friends stream. As such, you may friend an existing follower, but you may not follow and existing friend. This is because as friends, you both already have access to each other’s timelines.