I should write a blog post about this, but to those thinking about deleting Facebook, My experience deleting it 5 years ago is summarized as: my friend count went way down, my friend quality went way up. Your results may vary, but the purpose of my comment is not to immediately be worried that Facebook is a mandatory lifeline for your social life.
I ended up returning to Facebook and purging my "friend" list down to just a dozen actual friends.