Is user Subscribed field in user data

I have a Custom subscription form for my website and I want to know which users subscribed to the list. I plan to use an Checkbox weather user sync should add the user to the list or not, as shown in this code from here –> FAQ –> Only synchronize users based on a custom criteria

add_filter( ‘mailchimp_sync_should_sync_user’, function( $subscribe, $user ) {

// check for custom user field
if( $user->subscribe_me ) {
return true;
}

// do not subscribe otherwise
return false;
});

The problem is, that this box stays checked when a user unsubscribes from the list.
I think with the help of the mailchimp webhook this should be solvable, but I don’t know how. Or has anyone a better Idea on how to find out whether a User is subscribed or not