To answer your question from way back, your partner and new girlfriend would be "metamours" to each other.
I know there are a lot of definitions, but they can be useful in describing relationships. In times when a picture can't be drawn
I suggest doing a search (in the tool bar) using key words that you want to know more about. I don't go to "golden nuggets" actually. If ever I get time I'm going to put some threads on there that I am always looking for. I tag helpful threads more.
I have something in common with you LM, I'm dating a married woman and am married myself. I have a boyfriend too, Mono. Anyway, if I can help in anyway, please ask me
By the way, just because your partner *allows* you to be poly doesn't mean you need to be. Its your choice and there is no rush. It could be something to keep in mind, but not pursue right now.