Facebook friends can be lost for a variety of reasons, and it's usual for friend lists to change over time. You can be losing Facebook friends for the following reasons:
Inactive or Deleted Accounts: You may find that some of your friends have deactivated or deleted their Facebook accounts, which will remove them from your friend list.
Privacy Settings: If someone doesn't like the stuff you publish or wants to restrict who can see their own postings, they might unfriend you.
Change in Interests or Beliefs: Occasionally, differences in interests, convictions, or values can cause friendships—both online and offline—to diverge naturally.
Inactivity: If you haven't communicated with some friends in a while, they can decide to delete your name from their list of friends.
Online Behavior: People may unfriend you if you exhibit offensive, combative, or improper behavior in order to prevent awkward situations.
Social Media Cleanse: Some people regularly purge their social media accounts by unfriending persons they no longer consider close friends or with whom they have lost contact.
Misunderstandings: On social media, misunderstandings or poor communication can occasionally result in friends being cut off.
Account Security: Accounts may occasionally be hacked, leading to the unfriending of users or other changes.