I already posted once about my logical reasons for not believing in God, but I did not give the history of how I got there. It's a long one, and very personal, but I think a few people might be interested in it.
I'm going to share a few experiences I remember illustrating how my beliefs and doubts have changed over time.
When I was young, I received a lot of positive feedback for bearing my testimony. I set a goal to bear my testimony every month, and did so.
In high school I placed a lot of trust in my teachers, always attended seminary, and enjoyed it very much. I kept a 4.0 in seminary.
Around high school graduation, I became interested in whether evolution was true. I read two books on the subject: one was Faith of a Scientist by Henry Eyering, the other was Answers to Gospel Questions by Joseph McConkie. I learned that Henry Eyering believed strongly in the evolution of man, while Joseph McConkie said evolution was not compatible with Mormon doctrine. I concluded that either position was acceptable, because they were both prominent members of the church, so it didn't matter if evolution was true or not. I didn't read anything at the time about the evidence for evolution.
At BYU, my good friend James and I frequently discussed evolution. I read BYU's packet on statements from general authorities about evolution, and again concluded that it was fine to believe in evolution.
In the MTC, I read the entire missionary library, and bought interesting institute manuals from the MTC bookstore. Some things, like A Marvelous Work and a Wonder, and other people's testimonies, bolstered my testimony. Some things, like the Pearl of Great Price study guide, thinking about the Atonement, and stories about the Joseph Smith Papyri, caused some doubts.
I was sometimes skeptical of people's supernatural experiences. My trainer in Cambodia told me he had seen someone be possessed, and that the Cambodian witch doctors had the power of the devil, and I thought there was probably a more natural explanation for the stories he told me. I was skeptical about many people's amazing stories, if they involved angels or the devil, unless they were officially sanctioned by the church. I still believed strongly in spiritual promptings and inspiration. At one point during my mission, I decided that I would read an anti-Mormon book someday, because I wanted to know both sides. I didn't fulfill that goal until several years later.
After my mission my time and attention basically was devoted to girls and classes until my last semester at BYU. I received a certain copy of Wired magazine with an article about the "new atheism." It really piqued my curiosity, but I didn't dare read more about atheism while I was at BYU. It really appealed to the skeptical side of me, because I had long thought natural explanations of many stories were more likely than supernatural explanations, although I had not yet applied that logic to church history or God. Just after graduating, while on a road trip with some friends at Disneyland, I purchased The God Delusion. I hid it from my Mormon friends, but was excited to read it when I got back.
After returning from the trip, I began to read The God Delusion. I found it totally devastating to my faith. I found it totally convincing, and very depressing. Some mornings I was so crushed I couldn't even get out of bed. The thought of admitting to my parents that I was losing my faith made me feel sick. It was a very sad time in my life, and hard on my self-esteem.
I told my bishop I didn't want a calling, but a week later the First Counselor asked me to serve as a Family Home Evening (FHE) group leader. I would organize Monday night meetings for a few members of our singles ward. I had been taught never to turn down a calling, and I didn't have the courage to leave the church, so I accepted it. In retrospect this was a mistake, as it kept me in the church for years longer than I should have been. I often felt sick before FHE, terrified about bearing my testimony, terrified that someone would question whether I was being honest, even though I knew that would never happen. I also avoided dating until I decided whether to stay in the church or leave.
After about 2 years, I knew I was wasting my life with indecision, so I decided I would put more effort into having faith, start dating, and pursue marriage. At the time, I thought I wanted to remain in the church forever, even if I never believed with the level of conviction I once had. During this time I would occasionally admit of serious doubts to my parents, my bishop, close friends, or whoever I was dating. Sometimes I would think "you're really an atheist and lying about your beliefs," but I would try to push these thoughts aside and tell myself I had faith.
After about two more years, I decided to marry Sarah. At the time, I was not honest with her about how serious my doubts were. After we had been married a few months, I was serving in the Young Mens' Presidency, and I felt like the young men in the ward didn't have the self-confidence I thought they ought to have. I thought about how the church's teachings about masturbation hurt my self-confidence when I was a young man, and I was concerned about how the church was affecting them. I continued to feel sick when I had to teach gospel lessons. Eventually I admitted to my wife that I did not believe in God, and asked the Bishop to be released of my calling.
Admitting that I was an atheist was very hard on my wife, but liberating to me. She was at first angry that I had not been honest with her, but supported me being honest now. My self-confidence was largely restored when I found the courage to defend my true beliefs, even though virtually all of my friends and family disagreed with me. I finally didn't feel the need to hide or lie anymore.