How to Implement a Friendship Model in Rails 3 for a Social Networking Application?

I'm currently working on a small social networking application and right now I'm trying to create a model that represents friendships between users. This is what I came up with so far:

class User < ActiveRecord::Base

  # ...
  has_many :friendships
  has_many :friends, :through => :friendships

end

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => 'User'
end

My friendship model has a field confirmed as boolean which I'd like to use to define a friendship as pending or confirmed.

How can I access all pending request for a certain user? Can I somehow define this using Rails' scope method? Something like

current_user.friendships.requests # => [Friendship, Friendship, ...]

would be great.

How can I make this association bidirectional? Do I simply add another friendship once one has confirmed a friend request such that my friendship table would look similar to this:

| user_id | friend_id | confirmed |
-----------------------------------
| 1       | 2         | true      |
| 2       | 1         | true      |