If you are Firefox user i have recomended addon for your browser, its called "Greasemonkey".
one of it function is informing to you who was remove you as her/his friend on facebook
Just Install Greasemonkey Download link (https://addons.mozilla.org/en-US/firefox/addon/748/)
then restart your firefox, monkey face will appear on right bottom of your browser like this
and then install Unfriend Download link (http://userscripts.org/scripts/show/58852)
Click INSTALL and then restart firefox again, after restart open http://www.facebook.com like usual
Tarrraaa...... You'll have a new menu Called Unfriend
Done!!