So sorry you're having tummy trouble ! I hope it settles down soon ...
The FB anxiety is completely understandable . You're changing a habit that has become unhealthy . It will take a while before not logging in on impulse becomes your new " normal " .
As for the group ...cutting the cord is rarely a one step process .

I think you are doing right by using the " slow fade " . They'll adapt to your decision to be less present . You don't have to give it up completely if it's something you enjoy but stepping back a bit seems to be working for you . Good idea turning on the airplane mode !
Just remember that you make the rules for how much of yourself you are willing to give . That doesn't make you a selfish person . It makes you someone with healthy boundaries , both for you and for the people in your life . ( people
need boundaries ! )
I know it's hard to lose a good admin on a forum but even here , we all agree - our own well being comes first . We have said sad good-byes to some wonderful folks , but we are happy in the knowledge that they made a decision that is right for them .
No broken record worries ! Talking things out is healing and necessary . It's what we're all about here .