Do you want to know who removed you from her/his friends list on Facebook? You may have come across many Facebook apps that claim to tell you who deleted you from their friends list. But the truth is that none of them actually work. They are all fake/scams as it is against Facebook TOS for app developers to monitor friends. Facebook will immediately suspend any app that tries to tell you who removed you as a friend.
The only way to monitor this is to do this outside Facebook. Fortunately, there is a way, the Facebook Unfriend Finder. Unfriend Finder is a script that helps you monitor people who have deleted you from their friend list. Installation of this script is very easy. You can see the instructions for all the browsers here.
I recommend using Firefox with greasemonkey and using Unfriend Finder as a greasemonkey script. Learn all about installing and using greasemonkey scripts on firefox, and then download Unfriend Finder and install it in Firefox.
After the installation, you will see a new menu, Unfriends, on Facebook.
You won’t see anything when you click on this menu option now. But rest assured that it has started to monitor your friends. If you see a drop in your friends count after you have installed this script, then click on the Unfriends to see who has removed you as friends.