My first fic was A Year Like No Other. While it took me a while to give in and actually read the story, my friend worked on me for over 6 trying to get me to read any fanfic, I was hooked several paragraphs in. I spent the next few months learning about fanfic and reading mentor/adoption/severitus fic, then ran across a story where Remus and Severus got together...what an eye opener that was. You have to understand, I had never known fanfic was there. I had no idea, I was so in the dark about it all. Then to find out that people made "other" pairings, and some of them were gay...yeah, never looked back after that.
As for why Snarry. A Year filled a void that canon left. There should have been more between Harry and Severus, that was obvious by book 4. While I hadn't understood that void was there, I was greatful it had been filled, and once my slash blinders were removed, I found my first OTP! :)