How to Check Who Has Un-Friended You on Facebook

First of all Enable Timeline Feature in your Facebook Account.
Now open your profile and click on the year in which you want see the people who unfriended you.

Scroll down the cursor till you find Friends column where you wil see list of new friends you made in that particular year. Like in this screenshot you can see I Made 32 New friends.

Click on it and all your friends will be shown in a new pop-up window and if you find Add as Friend option next to any person it means he has un-friended you.

You can check all the years one by one to find out how many of your friends have un-friended you.

It's All Done.