First of all, thanks to everyone for your replies. I've been reading here for a few weeks and following a lot of helpful links to articles and websites about polyamory, and I know my story probably reads like a "what not to do" manual for polyamory.
Kevin, you're right that honesty and consent are essential...for any relationship. That is something that I am certainly struggling with. I'm on my way out the door right now but I have a lot more to say about that.