I've known I liked guys and girls pretty much since I started jerking off. This was back in the dark days before xtube and stuff where if you wanted to see real live 27 year old 18 year olds you needed to join a paysite, so I mostly "used" the free trial sections and the rest of the time free erotic story sites. The story site I used the most had a gay section and I don't even remember why I first looked there but I did and those stories turned me on just as much as the straight ones. I never really had any big "oh my god I like the cock!" moments except this one time that was only like "I think guys are really hot, am I gay? Nah, I like girls too, I'm good." and even though I liked guys I never really thought about having a relationship with one. I just knew that one day I wanted to have sex with a guy. So in middle and high school I did the dating girls thing enough to realize that, finding them attractive or not, I really, really don't like dating them.
So a bunch of years of not dating happened for various reasons and by the time I was ready to try a relationship again I figured "what the hell, might as well try it with a guy" and eventually met my boyfriend and we've been together for more than 4 years and counting Even if we broke up though I can't see myself ever dating a girl again. Being with a guy is just so much better in every way for me that I'd never be happy with a girl.
As for coming out, I didn't do that until about two years ago and I did it in an email to my mom while I was 480 miles away visiting my boyfriend that basically said "you know that girl I've been going out to Ohio to see for the past few years? Well, she's actually a guy. Tell dad ok?" They both took it perfectly fine. Well, my mom cried but she said it was because she felt awful that I didn't feel like I could tell her before then. They love my boyfriend and everything's all puppies and rainbows as far as my sexuality goes.