Thanks again to everyone for your advice and support.
Here's a little update. My bf and I went to a swingers club last weekend. I got brave and introduced myself to a couple women sitting together. They were both married with their husbands there also. We ended up having a great time together. My bf and I really liked one of the women and her husband. We even had a little make out session with the two women. I turned and saw my bf kissing one of them while I was with the other. I had a tinge of jealousy, but I was surprised at how well I handled it. Then he turned and kissed me, and I felt pretty darn good about the whole thing. He told me later in the night that this is just what he needs. I was so happy! I feel like I can give him what he needs now, and we will both be happy.
We traded numbers with the couple and have plans to see them this weekend. The funny thing is I think I'm more nervous about being involved with the other man than my bf is. I'm just trying to relax about it, and remember that I had no idea how the club night would go, but we made it go how we wanted. Anyway, I know that my bf will help me and make sure that I am always comfortable.
So it appears that my freaking out about an emotional polyamorous relationship was unnecessary, but I'm glad to have heard what everyone has to say. I think much of it still applies to a mostly sexual relationship with others, and I will still be growing and overcoming insecurities. I feel much more confident now, though.
Thanks and Smiles.