It's on the Wikipedia page for Polyamory, in the section on Terminology. And one of the links there goes to an archived version of the Ravenhearts' website where that quote came from. They have changed their website, so it isn't there anymore, but is preserved by archive.org's Wayback Machine.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein