someone who DOESNT talk about you behind your back, someone who lets YOU know if others do talk about you behind your back (even if it hurts), someone who tells you the truth about how you look or what your doing with your life(even if it hurts), someone who tells YOU if they hang out with your ex boyfriend who they never liked when you dated him even though you say you could care less about him, and finally someone who laughs at your jokes, doesn't look at you like your a total idiot when you tell a stupid one, and cries with you when your sad and doesn't just sit there and say they don't know what to say or avoid the subject...
One who looks after your best interests - would never do anything to intentionally hurt you or cause you embarassment - supports you when you're right but lets you know when you're wrong - CARES !!
someone you can trust with your secrets. someone you can talk 2 and they are always there. and they are not mean. thats all I can think of