Using FB as your Private Forum

Dear Cybersorter,
I blog and I tweet so I keep my Facebook to only 70 friends and all my settings on “friends Only. This is my private forum.
Yesterday I saw a tweet, from a guy I didn’t know, reporting something I had said on FB. I discovered he’s a friend of only one of my friends. So my FB friend must’ve told him what i said.
This, for me, is a defriending offense. On the other hand the friend was super nice to me in the past. Should I defriend?
Your privacy is only as good as your big mouth friends.
Exposed

Dear Exposed,
You are right. Whether your relationships are on-line or face-time, people, even friends, will occasionally betray you. However, there is a difference between sitting at the kitchen table over a cup of tea, saying “this is in a cone of silence” and confiding in someone, and writing it up on your Facebook wall.
Many assume that what is written on FB is intended for public consumption and fair play. That doesn’t mean that they shouldn’t check with you first, but some of your FB friends are there because they like you and some of them because they like being connected with you.
In your email you alerted me to a handy tool called http://www.reclaimprivacy.org/facebook, which checks for holes in your security settings. There’s no safety bot for weeding out your more self interested “friends”. However, this one has now exposed themselves and despite past kindness, unless it was saving your or your dog’s life, you can and probably should defriend.