Did you ever think about the fact that many of our friendships are 'accidental?' For most of our lives, the people that we meet are defined by our social context at the time. As a result, as we reach our 50s, we often find ourselves with people in our lives that are actually causing us more harm than good.
Just as one would never go into a marriage with the expectation of it leading down that bumpy road of divorce, the same applies to friendships. You go into friendship eager to forge what you hope will be a lifelong bond with that person upon whose shoulder you can lean, let down your guard and be as silly as any nonexistent law allows.