You don't need a UserUser model.

class User extends Eloquent{

public function followers(){//they follow this user
return $this->belongsToMany('User', 'user_user', 'id_user', 'id_userseguito');
}

public function followings(){//this user follows them
return $this->belongsToMany('User', 'user_user', 'id_userseguito', 'id_user');
}
}

Check if it works.

$user = User::find($id);

$followerNames = array();
foreach($user->followers as $follower){
$followerNames[] = $follower->username;
}

$followingNames = array();
foreach($user->followings as $following){
$followingNames[] = $following->username;
}

return array(
'user' => $user,
'followers' => $followerNames,
'followings' => $followingNames 
);

De nada :P