In my vernacular you're one of us ... Polyamory is a large word, and it covers a wide range of lovestyles. You'd be surprised how many people "fall into poly," rather than deciding ahead of time that's what they want to do.
I know you must feel scared and disoriented, but feel glad that your husband is very supportive, and that cute-girl is your friend regardless of whether you and she develop a romance with each other. I think you're fortunate. I'm glad for you.
Have a look around at our various threads here; there's so much to learn. Do's and don'ts, what to look out for, what to look forward to, all of that.
Tell us more of your story, and let us know what thoughts, questions, or concerns you may have. Above all, live in the moment and find joy in it.
Glad to have you aboard.
Love means never having to say, "Put down that meat cleaver!"