You are proceeding from a false assumption. At no time in my life did I have a belief in the reality of any gods (which I imagine includes whatever one you believe in), so it is not a matter of not believing “anymore.” You might similarly ask yourself, at what point did you come to believe in the particular god you believe is real? Was that the one of your parents or cultural group? If you had switched gods along the way, why do you think that?
There are certainly many mixes of how and why individuals end up with the beliefs they do (and remember, no matter which god you believe to be true, or how generally popular that believe may appear to you in your cultural frame, most of the people on earth do not share your belief, and this has been the case all through human history).
I’m not Orthodox, or even close. So I posted your question in a Facebook group I’m a part of called God Save Us From Your Opinion: A Place For Serious Discussion of Judaism, which I know many Orthodox Jews are members of.