Actually about half of the internet uses use Facebook every single month. If you include the number of people with a Facebook account that do not use it monthly

Actually about half of the internet uses use Facebook every single month. If you include the number of people with a Facebook account that do not use it monthly, that total number is obviously higher, not lower. Since your link estimates 3.4 billion users (half of which is 1.7 billion), and 1.65 billion use it every month, that's almost exactly half. Again, this is only monthly active users, and not total users.