I agree with EugenePoet.
Personally, I don't identify as poly, or as mono. I just happen to be a person who enjoys making emotional and physical connections--and sometimes they're monogamous, sometimes they're not (like the wonderful poly relationships I have now.) Because I cycle between the two, I often find myself feeling limited in mono relationships, and when I'm in poly ones, I find myself wondering things like, does it bother Jenny to come home from work and find me in bed with Alex? I think it's the nature of polyamory in this society where so many songs, books, and movies emphasize the need for "the one" and that any sexual or emotional intimacy outside a primary relationship is "cheating." There's no easy way around it, and it might be that devil on your shoulder for a while.
All you can do is be open with your husband, encourage him and your good friend to give honest feedback, and try your hardest to make him feel special, singular, and important when you're with him and not with SNBF. There may be some jealousy issues, but as time goes on and you all become more comfortable with the idea, these things will subside.
In the meantime, though, do enjoy your NRE. It's hard when you want to explode and tell everyone how happy you are, especially when you don't think half your friends will understand it, and the other half won't be okay with it. I think that's why some of us are here--at least on these forums you have a place where you can express your happiness unabashedly. So go ahead, and squee as much as you need to, hon. The internets are listening.