Facebook algorithm is an enigma.
It seems that, to have someone’s posts appear in your feed, and yours appear in theirs, you and that person need to like the other’s posts, or share them, or comment on them. But if you are not seeing the other person’s posts in your feed, you don’t click like and you don’t share and you don’t comment, and you probably forget you were ever Facebook friends, so they disappear into a black hole.
And whose fault is that? Mr Facebook?