Hmmm, how I found out about yaoi? Well, I believe that it first started when I watched my first anime, Sailor Moon and I noticed that Amara (Haruka) and Michelle (Michiru) were definitely NOT cousins (afterall I first watched it when it was aired in English). After that, I started to look at other shows I liked to see if there was anything else of the sort.
When I heard about Gravitation, my mind flipped. I was excited that there was an anime and manga about two guys in a relationship! I knew I needed to have it, even though I wasn't too sure why at the time.
So, I guess from there on out, my love for yaoi just kept expanding and I started noticing things about anime that some of my friends never noticed (those of my friends who like anime). Then I started to read slash fanfiction and actually came out and asked my friends, do you know what yaoi is? Not many of them knew and it was fun and kind of awkward trying to explain it to them.
I guess you could say that Sailor Moon opened me up to yuri and yaoi. Who would've guessed?