I'm from the Bible Belt as well. My suspicion is that you actually do know some atheists, but you just don't know it. It's very difficult for atheists to be "out" in the Bible Belt.
As to your question, I would first just point out that it's less that I "decided" there was no God, and more that I just "realized" there was no God. And for me at least, it wasn't "liberating" so much as terrifying.
I wasn't frightened of God's judgment or anything like that. Having grown up in a fundamentalist Christian household, I was always taught that doubt, in itself, was sinful, so by the time I got to the point of not believing, I had already crossed the line of doubting God (and thus being subject to judgment) long before that. In that sense, when I finally realized there was no God, it actually erased any fear of judgment - there's no God to judge me, thus no fear.
Instead, I was terrified of the reaction that I would get from people around me when they found out that I no longer believed in God. My number one concern was my grandparents, whom I am very close with. I knew that it would devastate them, and that was really tough for me. (To this day, I have never really "come out" to them, although my parents told them - something that I honestly think I will always be resentful towards my parents for.) Beyond that, literally everyone around me, friends, family, my whole community really, were Christians, and so there was a deep, deep sense of loneliness when I realized that I had basically become "evil" in all of their minds.