I'll try help you understand.
A large portion of churches try to teach that homosexuals come about from bad experiences as a child, bad fathers, or bad mothers. They sometimes teach that a child will experience an act of "deviance" with another child, and as such some much enjoys that feeling of deviance, that the child will repeat the actions until he/she is addicted to that, and somehow loses attraction with the opposite sex.
These theories are taught to their congregations and the congregations suck in that information because the pastor is always right, and they don't know the real truth.
The truth is, speaking from my experience is that from a very young age, in my case, from about 5 years of age, I was aware that I was attracted to the same sex. At that age, I wasn't sexual, I didn't know what sexual attraction was. All I knew was that I was fascinated by the bodies of the other boys in my school class. I had no interest in girls. I believed that that was the norm for most boys at that age. I'm not sure if that is true or not.
However,
There was no bad mother, there was no bad father, I was not molested, I never saw any porn, I never never played with out boys in a "naughty way", nothing. In fact, my first sexual experience was only last year.
I grew up in a Christian family, I went to Sunday school every week, I got my first real bible when I was 6 years old. I prayed to God regularly, and I lived the life of a little Christian boy.
When puberty arrived, all my friends started checking the girls out. My hormones started developing as per the others, but I never ever had an interest in checking another girl out. However, the boys fascinated me. Obviously I kept that to myself, because I felt that it was something that nobody should know about me. I never had access to porn, I never ever had an experience with another boy. My mom and father were wonderful parents as they had always been.
At about the age of 16, I knew without a doubt that I was different from my friends. Due to my sheltered upbringing I didn't understand why, because we didn't know about homosexuality. I didn't know what was happening to me, as a result I kept my feelings to myself.
By the time I was 18, I was still under the impression that my attractions to the opposite sex was just a bit delayed, that my feelings for the same sex was what every boy experienced. I didn't know what a homosexual was.
When I was about 20, I still believed that I was a late developer and that the perfect girl for me would appear from somewhere. However my attractions for the same sex became very very strong, and were difficult to bury down. I spoke to my pastor and he confirmed with my opinions at that time that it was a normal "phase", and it would go away eventually. By now I'd heard about gay men, but I didn't consider myself as one because I did not seem to fit the profile. I was a guy, I did guy things, every action of mine was the same as all my other friends. Except for one difference it seemed.
I spent the next 10 years waiting for that phase to go away. Obviously it didn't. During that time, I had one girlfriend, who I was not sexually attracted to. We never even kissed. I'd never had any sexual contact with anybody.
Until 18 months ago, I never made a choice to be attracted to one or the other. If anything I had made a choice to try to make myself attracted to the opposite sex. After all, that's what guys are supposed to do. I went on a few dates with girls, in the hope I'd find one that I was attracted to.
I realised that something had to be done about my problem. I simply was not becoming attracted to the opposite sex, regardless of all my efforts. I would shout and curse God, then ask him for forgiveness for me shouting at him. I'd pray for the right girl to come into my life. I'd pray for my attractions for guys to go away. I've lost count the number of times I'd pray.
The "realise" you speak of, is more the acceptance of who you are, more than a choice. There is no choice, for me, I know I never ever had a choice. It's mind boggling when I here these so-called theories about gays making choices etc, because I know it is simply not true. At no time did I have a choice.