Technically I never was a muslim since I had doubts from the beginning.
I didn't hear much about religion until I was about 4-5, then my family suddenly started telling me about heaven/hell, Allah and all that. At first I didn't believe them at all but they told me that if I question it, it'll be a sin and i'll go to hell, so I started believing it.
Then there was a period when I was 10/11 and my hormones were building up, that I was really jihadist, supporting osama bin laden & taliban, etc just the way I used to idolize He-man, Superman etc before that. I'm very thankful to my elder brother who basically woke me up and taught me about concepts like racism, secularism, etc which I had never heard of (I suspect he is also an agnostic/athiest though he hasn't told anyone, and neither have I).
Then I was still a muslim for a while though I didn't like saying prayers and all the religious duties, and looked for excuses to not do them (i basically very rarely said prayers and that too only before exams and such
). Furthermore i had a growing attraction for girls, and then guilt as I tried to suppress it, and one day when i was 14-15 I just asked myself that if Islam were really true and god had created me, then sexual attraction must also have been created by him. So it would be OK if I had sex or watched porn etc. Plus I learnt more about how it was a biological desire experienced by everyone and not something I personally created and need to feel guilty about. This also started making me doubt many other things in islam.
Until last year I was in that state where I still called myself a muslim and believed in the core aspects of the religion, but I never prayed, did whatever i wanted to do, had a few girlfriends, etc (though i didn't drink or eat pork, and still haven't). Then last year I learnt more about evolution and I researched it, and found that it was proven that humans evolved rather than being sent in as adam & eve. Furthermore I found out about the many contradictions in quran, and in religions alltogether. All of this I found in perhaps a few weeks. And then I basically decided to abandon it for good, and that no god was going to smite me and send me to hell for it. And i've been feeling liberated since
.