how do i know if someone unfriended me on facebook?

[Snoop D O Double G]

I cant say about the app but what i know is when someone blocks you just search in your friend list whether you can see them , if you cant see them then search them in the search bar and even if you cant see them then they have surely blocked you but to make sure always advisable you search for them from other account to confirm that they have blocked you else it can also be that they themself have de activated their account because you cannot see someone when they de activate their account . hope it helps!