On Facebook, you need to download Deleted. This application, which includes an extension for the Chrome browser notifies you every time you lose a friend. What is good is that Delete is able to tell you if someone has removed you from their friends list (it does not want you) or if he just closed his account (that is less worse).
How do I know that someone has unsubscribed from you on Twitter
Twitter is pernicious because you can follow someone who does you not follow. This is the same tactic of many people, especially those with tens of thousands of subscribers. They subscribe to a variety of accounts, then, when the people have subscribed in return it to unsubscribe. It’s dog, but legal, as they say! Fortunately, you can know who is playing that game on Twitter through Who unfollowed me.
How do I know that we have unfollowed your account on Instagram
Unfollowgram works much the same way as who unfollowed me. He can tell you who has unsubscribed from your account.