I hear ya, EW. I had a similar upbringing and still have challenges despite having had a spiritual epiphany and experienced things that would indicate there is something to what mystics of all religions have been saying all these years.
As usual, I agree with ES. The existence (or non-existance) of God(s) (assuming we could clearly define for ourselves what God is) may be impossible to prove but, as far as I can tell, no one has seriously tried to apply science to answer that question because they don't know how. The closest people have come is through noetic sciences, which don't tackle the God question directly. So I'd have to say atheism is based largely on a belief rather than on evidence or lack thereof.
Even if you based your belief completely on your personal observations and you thought you had found no evidence to support a belief in God, coming from a purely atheist or agnostic viewpoint, would you ever be able to have those? What I mean by that is, I think one must be at least be truly open to the possibility of an experience of God in one's life in order to see something as an expression of the divine. It is extremely easy to write off most supernatural (for lack of a better word) experience with a "scientific" explanation though no science is actually being applied to test anything.
My advice would to ask yourself why you feel you need to believe in God if you do. What purpose does it serve? And conversely, if you feel a need to believe there is no evidence for God, what purpose does that serve you? And then compare the two and decide which standpoint does you more good. Because I think what you really are doing is trying to decide which belief system is a better fit for you.