For me personally, I've never doubted it but when I first realised I was gay I denied it for years and even dated girls hoping I'd find something that was special enough to change me but that didn't happen. I was bullied at school for years because of my sexuality (this was before I even came out) which made me want to hide it even more. When I finished high school I realised that it's not anything to be ashamed of and no matter how much I wanted to be "normal" I never was going to be so I came out and I haven't looked back since