Currently Facebook does not give out information about who has removed you as a friend. There was a bug on Facebook Timeline that allowed you to see who had unfriended you but Facebook has removed that bug by now so if you happened to read some tutorials that teach you how to find out who unfriended you by using Facebook Timline then that method is not working anymore.
There is a Free App however that would show you the following:
Which friends have removed you.
Which users have deactivated their Facebook accounts.
Which users who you have requested friendship with have declined your friend request.
This App uses Facebook notifications to alert you about these events.
This App is called Unfriend Finder and it is compatible with Firefox, Google Chrome, Safari, Opera, and Internet Explorer. It is very simple to install and you will get a lot of instructions on how to use it, as well as a setup box. This app however is not retroactive, it means that it will only track unfriends starting form the point you had it set up and not in the past.