Don't do it. Being honest with people doesn't mean you have to tell them nor do they have the right to know everything about you. They know what kind of person you are by how you are when you are with them. Does it really matter that you don't believe any more? Will it be helpful or harmful to them and to you?
I think if you can resolve it with yourself that you do not need to share this detail of your life, things will be easier for you and for them.
my 2 cents,
bafh