I guess the first part of it is when I was 9 and we moved away from New Jersey. In New Jersey we used to go to Etz Ahaim synagogue on a regular basis. I went to Hebrew school there every week and we attended all the high holy day services there.
But then when we moved to Waldport, with the nearest synagogue being well over 100 miles away, in Portland, we no longer went to services at all. My parents got me several tutors over time to help prepare me for my bar mitzvah, which we also had at Etz Ahaim in the summer when I turned 13, for which we flew across the country and stayed with my grandparents.
Looking back on the tutoring, though, it was focused solely on my being able to read my Torah portion. During that time I didn't learn any more about Judaism, being a Jew or even Hebrew vocabulary, only what I need to read my part, without understanding it. And to keep from taking it appropriately seriously, my father used to time me with a stopwatch when I was reading it, always pushing for faster and faster times as the goal, rather than the usual, normal sing-song rhythm.
Sometime around then, too, my parents started making me earn my TV time by reading "approved" books. For that I had to read 45 minutes for every half hour of TV I wanted to watch, in advance. Most of the books my mother picked were about the Holocaust.
And there, I think was another major reason I lost my faith. How can a youth read all those books about death and murder, with little or no guidance, and still think there really is a God?
As I became a teenager, while not consciously thinking about not believing, I was also reading a lot of swords & sorcery literature and some horror. For quite some time I felt H.P. Lovecraft had the perfect description of what I thought in the story Herbert West -- Reanimator, in which he states 'that all life is a chemical and physical process, and that the so-called "soul" is a myth.'
There's times when I think about what I believe and I really hope I'm wrong, that there is a God, heaven and all that stuff, as the idea of absolutely nothing after death is kind of full. But there's quite a difference between hope and actually believing, and I simply don't believe.
And seemingly at odds with that, I do enjoy some of the rituals of Judaism, and symbolism. That's in some ways part of my identity, as I grew up with my family celebrating the Jewish holidays and going to services, at least before we moved to Oregon. In that regard, one of my favorite stories is about Hillel the Elder, who was challenged to teach the Torah while standing on one foot, and he did, saying "The whole of the Torah is to treat others as you would be treated, the rest is just commentary" (there are quite a few variations on the story, whether it was him or his student who stood on one foot, and slight changes to his actual quote, although they all have the basic idea.)
With further thought I've come to decide that I believe in God as a symbol, but not as an entity.