Flags to create mutual friends?
You can do this by using Flag Friend module


  Flag Friend aims to be a lightweight friending module utilizing the
  excellent Flag module's API.


Or

Flag Follow


  This is a simple module which allows a user to view Heartbeat
  activities of his favorites/followed users. A user can add another
  user to his favorites list by just click on a 'Follow' button. It
  requires no approval to add a user to your favorites list.


or

You can do this by using Follow module.


  Follow adds sitewide and per user links that link to various social
  networking sites. The links reside in two blocks. The Follow Site
  block lists all the links for the site itself, and by default is
  visible on all pages. The Follow User block lists all the follow links
  for the user and is visible only on user profile pages.