My journey started with me reading the Bible cover-to-cover, because I wanted to deepen my faith. I couldn't believe or reconcile what I read with the idea of a loving God that I'd been taught, so I started asking questions of my youth pastor. Neither he nor my pastor were able to give me satisfactory answers, so they suggested I read Lee Strobel's "The Case for Christ".
Today, I credit that book with the loss of my faith. I learned what a fallacy was by googling the problems I had with his arguments. After a lot of debate, I decided to stop calling myself a Christian. I figured I must have been raised in the wrong religion.
So I started researching other religions. I got my hands on copies of the Quran, the Baghavad Gita, the Book of Mormon, and some texts on Kabbalism.
I had the same problems with every religious text I read as I had with the Bible. I had included the Internet in my research, and I discovered that not believing in a deity was an option. I had been taught that atheists were people who worshiped Satan.
So, I stepped back from my assumptions and decided to look for evidence for a deity. After all, if some deity existed, and this deity interacted with the world in any meaningful way, there would be evidence. If this god answered prayers, for instance, then we should expect that its worshipers would be, on average, healthier and happier. What I found was numerous studies suggesting that prayer had (at best) no effect at all.
I finally decided that my underlying belief that a deity existed was unfounded. Today, if a theist starts a conversation with me about belief, I'll still ask them to present their evidence. So far, no theist has been able to do so.