There is one true test to find out how tenacious or how tenuous a person's friendship is, whether it is a real-life friendship or merely a Facebook friendship:

1) UNFRIEND that person without rhyme or reason.

2) After one week, send him a Friend Request without any Message and without any kind of explanation. See how he responds.

3) If he is oversensitive and his feathers were ruffled the first time around, he wll not Accept your Friend Request. Thus his friendship was tenuous to begin with. Be grateful that you lost a friend who thinks too highly of himself.