I fully understand your social life is not the same as my own, but mine revolves almost entirely around Facebook. Every party I go to is organised via Facebook. Every small social event is coordinated via FB Messenger. I maintain a large network of friends around the world who o can and do visit when I travel, and it's not weird because they're up to date with my life and I'm up to date with theirs in a way that would take far far too much work outside of FB. Every baby photo from a friend, every wedding photo, is on Facebook. When I meet someone in person and enjoy their company, we connect on Facebook, and it's a low pressure way to keep in touch that often blossoms in to a real and fulfilling in-person relationship.
I realise not everyone's social life is like this, but for many many people, there would be a severely restricted in-person social life by not being on Facebook.