My path to becoming an atheist was a somewhat long one, but I'll try to keep the story as short as I can.
I was raised in a Roman Catholic family, and was sent to Roman Catholic Elementary School and Roman Catholic High School. All my family and teachers were Catholic, as were the vast majority of my friends.
I think when I was young, I truly did believe what my parents, teachers, and other adult authority figures told me about faith and god, but over time my belief in what they were saying started to wane. I found mass to be boring and pointless. It was probably my undiagnosed Attention Deficit Disorder (Inattentive), that was causing that, but if so, it also caused my natural curiosity to come into play, to examine what was going on around me, and the claims of the people who were supporting the faith. I began questioning everything, using what resources of logic I had at that age. There were large sections of the literature, the ideals, and the practices that just didn't make any sense to me and left me wanting.
By the time that I was in high school, my belief was that universe was created by God, but after that, he no longer involved himself with it, letting it go on its own. This made sense to me, and answered a lot of question for me, such as why bad things were allowed to happen. "God's Plan" that I was told about didn't sit well with me. Was a God that included horrible things in his plans truly a good God, worthy of worship? I was told that we can't know the mind of God, but if we were created in God's image, that can't have meant only physically, it had to mean mentally as well, so why would our thinking be so foreign from his. We must be able to know the mind of God, simply by thinking. Well, after it all, it made more sense that he had nothing whatsoever to do with it, and nothing whatsoever to do with us or the world around us. I had one friend in high school who was an atheist, and he was the first atheist I met. He wasn't shy about his position, but religion wasn't exactly a common topic of discussion for us. Still, meeting him was my first introduction to the idea that there may not be a God.
As I continued to examine my beliefs and question things, by the time I started University, I was an agnostic. As far as I was concerned, there was no way of knowing for sure if there was or wasn't a god, and as I still held the belief that he did not interfere, it didn't matter anyway. Going through University, meeting more diverse people of a greater variety of backgrounds and faiths, I examined other spiritual paths, just to see if I was really missing anything, but none of them sat right with me. All of them fell short in some way or another.
I have always had a great interest in mythology, and I had read about the hundreds of gods humans have worshiped, in cultures all across the world, across the vastness of human history and yet now, only one of those gods is worshiped by the majority of the population. Those ancient peoples were convinced of the existence of their gods, just as people today are convinced that the Christian/Jewish/Islamic God exists. Delving into the history of Yahweh, in response to a debate with a friend, I read about the cults of Yahweh, Baal and Asherah, and how they existed at the same time, in competition with each other in the same culture, and how the cult of Yahweh was the lesser cult, with the worship of Baal and Asherah being the dominant faiths. It was only when the cult of Yahweh violently overthrew the other two that worship of Yahweh dominated and went on to spawn Judaism/Islam/Christianity. So, there was not even any kind of centralized worship of this one god to make him any more special than any of the gods now dismissed as mythology.
That was my 'tipping point' to commit to atheism. I am fortunate enough to have met a wonderful woman who shares my views, although she was not raised with religion or faith, thus has always been an atheist. The place where I grew up, issues of faith were of little importance to people, but living in the US Southeast, faith is far more important to people here. My employers and co-workers do not know I am an atheist, and the majority of my friends here are Christian, and none of them know about my views on religion. It pains me to say so, but I do believe that if I told them, I would be ostracized at work, and I would lose several good friends over it.