Code available at https://github.com/bryantt927/friend
Very simple “friend” module built upon Flag module. Need to create a user flag called friend. Then install this module. It will create block for friend activity. The block contains a table with two columns: friend requests (with a link to add the user as a friend), and a friends column. Principle is a user clicks the flag on another user, that is a friend request. If two users each click the friend flag on the other’s profile page, they are friends.