To give the short version, I was raised in the church of Christ, which is a fundamentalist Christian church. They taught the Bible was the literal word of God and that homosexuality was a sin. Eventually I realized I was gay and no matter what I did, I couldn't change my sexuality. I was afraid God hated me and was going to send me to hell and I couldn't understand how a loving God could torture people for all eternity.
I then started to study the Bible more and I came across biblical passages that depicted God committing the most horrific immoral acts anyone could ever do, like how he commanded the Israelites to murder children, rape virgins, and demanded that women marry their rapist. I've asked biblical literalists to justify God's immoral actions countless number of times and so far I've never heard a reasonable explanation that justified it.
Eventually I reached three conclusions: that either God existed but was evil and desired to see humanity suffer, God was real but was unconcerned if we worshiped it or not, or God didn't exist. I then thought that if God existed but didn't care if we worshiped it or not, it would be ok to not believe in it and so I eventually let go of my belief in God.