Amazing advice, Phy and redpepper. If I decide to take this further, I will make sure that we all take very small steps and process as much information as we can before making any decisions. I'm going to check out "Opening Up" and see if it's something they might be interested in reading.
As far as approaching my girlfriend with any literature, it may take me a bit of time to come up with a natural way to show it to her. I'm a little worried that, based on her previous decision that she'd be too jealous to handle a polyamorous relationship, she would become scared and concerned with the knowledge that I am researching the subject. This is a tough situation for me.
I will continue to think about this and research and hopefully figure out the right thing to do. Thank you very much.