I've just discovered this weekend that a friend has lied for years about something that isn't important to me, but is important in the context of her life.
I don't exactly feel betrayed as I understand why she lied, and it was a lie going back years but it's shaped how I look at her now. It's a bit like finding out something from your past and applying it to memories and looking at them in a new context.
I don't know why I feel so strange about it; it's not my business.