Self-referential MtoM implementation

ok, guys i have followed the self referential recipe from the book it
works perfect but now i have some doubts, at the end the model are
modified to force the user beign added as a friend that add too who are
adding him so how i can make that the full relationship doesn´t be
complete until the friend beign added approves it(talking in the
implementation of the code of course)?

by the way, here is the code:

class AddPeopleAndTheirFriendsRelationship < ActiveRecord::Migration
def self.up
create_table :people do |t|
t.column “name”, :string
end
create_table :friends_people do |t|
t.column “person_id”, :integer
t.column “friend_id”, :integer
end
end
def self.down
drop_table :people
drop_table :friends_people
end
end

class Person < ActiveRecord::Base
has_and_belongs_to_many :friends,
:class_name => “Person”,
:join_table => “friends_people”,
:association_foreign_key => “friend_id”,
:foreign_key => “person_id”,
:after_add => :be_friendly_to_friend,
:after_remove => :no_more_mr_nice_guy
def be_friendly_to_friend(friend)
friend.friends << self unless friend.friends.include?(self)
end
def no_more_mr_nice_guy(friend)
friend.friends.delete(self) rescue nil
end
end