Is there a way to find out who "unfriended" me on Facebook?
Intentionally, Facebook prevents sending out this info for privacy purposes. You are free to keep track of your friends though in some other form, and compare it to the current list to find out who is missing each week.
who.removed.me will do this for you automatically
Sites like who.removed.me will keep track of your friends list and compare it automatically.
One way to keep a log of who has added you as a friend is to enable email notifications. Then create a filter so it doesn't clog your email inbox.
It wouldn't really be practical comparing all these email messages to your friend list, especially if you have hundreds of them, but if you want to check if you were ever friends with someone, you could just search your mailbox.
If using Firefox the Greasemonkey plugin has scripts that will allow you to see this information right on the Facebook dashboard. The script I use is: Better Facebook
There's an app for that: "Who Unfriended Me?"!
It compares an old list of your friends with a current list of your friends, so that it can show you who unfriended you!
Also, the Unfriend Notify browser extension for Firefox and Chrome can show a pop-up notification when someone unfriends you on Facebook. It also adds a new tab section for "Lost Friends" in the Friends page, which will list people who have unfriended you.
Another option for finding out who unfriended you is the FB Purity browser extension. It also has a built in deleted friends notification system, that alerts you if any of your friends remove you from their friends list.
Try http://truefbfriends.com—It will tell you who are your real Facebook friends and who are fake Facebook friends. It will also give you data like how many likes, comments, mutual friends and chats your friends have done with you. It will also tell who removed you. A perfect website to filter your friends on the basis of interactions.