When A Friend Comes Out Of The Closet.This kind of things are rather wonderful, because coming out is an act of bravery. If a "straight" friend would tell me that he /she is gay/lesbian/bi, it would be a really nice progress, because that means he/she considers I am trustworthy and a good friend.
Should I trear him/her different from now on? absolutely NO! he/she has been like that during his/her entire life, there's no reason for that.
If a friend of yours comes out to you, first of all, don't freak out (in fact, you should be happy for that), show him/her your support and love as a friend.