I just grew up. I have always been interested in science, and learning about nature, in particular astronomy, somehow showed me that a god was not necessary to make things work. The “
problem of evil” also had a big part.
I was still going to church regularly (I assisted the priest as a ministrant), and I had no enmity against the church, but my belief just trickled away without me noticing it. Well, I had no love for the catholic church as an institution (quite the contrary), and even though the people were all very nice, the maltreatment of some people I knew perhaps also contributed a little to my gradual de-conversion.
It proceeded in stages. At first, I thought that God was perhaps not looking everywhere where a catastrophe, or injustice was taking place, and later I definitely thought that having created the world, God had fallen asleep in his armchair and was not involved in anything that happened, and finally, the armchair was empty – there had never been a god in it.