Specific procedure I’d recommend is to make this a regular process: open fb feed, read until you find a thing which does not improves your life, click on owner (author / group) -click “friend” -> unfollow. Iterate until sanity is restored.
And one moral of this story (hi Facebook, please understand this) is that people are multidimensional. Just because you know someone once, in one context in real life, does not, actually, imply positive relationship on informational ecologies for all time in the future. “Authentic self” as defined by Facebook as a single coherent identity is a lie.