I stumbled onto Paranormal Romance via Buffy.  I was/am a huge Buffy fan (though not as active in the fandom as I once was.)  I was a HUGE fan of the Buffy/Spike relationship.  The show didn't really "pay that off" for me (or a lot of other fans.)   So I went online to talk to fans about the show.

I stumbled upon fanfic, read a LOT of it, wrote some of it, and then when I got a little burnt out, I needed something else to read that was "like it, but not really."

This was how I discovered paranormal romance.