Facebook - How to know who unfriend you long long time ago

Note:
If someone block you after unfriend, it still possible to see post by create new account which only added you, so there are still some possibility it will shows post of friend of you.

There are actually 2 privacy bugs here.

First bug is the search able to store deleted comment in plugins( and probably also apply to other places I don't noticed). The first bug shows the over powerful of search by post leads bug.

The second bug take further step of first bug which tick on filter by "Your Friends". This bug proved that the friend relationship never drop even after unfriend, which actually also happen if the new account add only you and unfriend you then the friend suggestion more likely is still your friends.