There's No Such Thing As An "Ex-Witch"...
In truth, an Ex-Witch is nothing more than a christian who, for a short time, wanted to get a rise out of their friends by being a "Weekend Witch". And shortly after they got bored with it, decides to use it to once again get a rise out of people and fulfill their own ego with a new found higher sense of superiority over others.
A Weekend Witch is a derogatory term used to describe a person who claims to be a Witch after reading half a book on Wicca and buying a pentacle at the local Hot Topic. Some christians actually claim to have been a Witch because they once used a Ouija Board, shuffled a deck of Terrot Cards at a teenage friend's sleepover or even something as benign as lighting a red candle.