If you'll allow me, let me pose a question to you. You used to be a Christian; What made you lose your faith in God?
Basically, I stopped presuming there was a god and I started allowing for the possibility that gods aren't real.
I was born into a Christian family, so I became Christian. I would have been Muslim if my parents were Muslim, Jewish if my parents were Jewish, etc. I didn't question if that was the correct religion because that was the religion of my fathers.
A few years ago, I did a cover-to-cover study of the Bible that took about two years to complete. We went through every book, every verse, and really studied it. Combined with my interest in history and my knowledge of gods, myths, creation stories, and history in general, it became obvious that the stories in the Bible were just modified versions of the same stories that were being told by every other Middle-Eastern people at the time of the events in the Bible.
Combine that with a glaring lack of a god in our daily lives, and the whole "God is a loving father" story fell apart. Loving fathers are tangible presences in their children's lives. The Christian god is not, despite verse upon verse claiming he is.
During all that, I was frequently engaged in conversations with Atheists in which I defended Christianity over and over and over. Like water dripping on a rock, that constant defense of the indefensible wore away at my dogmatic beliefs and I allowed for the possibility that I wasn't right. I started considering their points rather than immediately dismissing them, and the point that god isn't real became more understandable to me.
It wasn't an instant decision, it was born over time and much thought.
I am far more convinced that the statement "there is no god" is true than I was ever convinced that the statement "God is real" is true.