Thank you again for all your words of caution. I shared all this information with my wife, including the link "http://www.polyamory.com/forum/showthread.php?t=4300&highlight=moved", to make sure we pay heed to it. I want to make sure this relationship works.
Fortunately, my wife and her new partner were the ones that originally approached me about forming a poly relationship, so they should generally be committed to the idea. I was the weakest link since I was (a) in shock, (b) felt betrayed, and (c) a staunch mono. If anyone was going to spin out and leave the relationship, it would have been me. Much to my surprise, I came around not just accepting the relationship but *LOVING* it. It feels like an awakening in me, opening my eyes... dare I be poly myself??
So now my wife's wife is the most mono in the relationship, and I want to make sure she feels welcome, secure, accepted, and supported. (I know what it's like to be mono!) For example, she was originally willing to accept her role as a secondary (even though she'd want to be an equal) in order for me accept the poly relationship. But I've taken her in as a full primary, equal to my wife and I in the relationship, and wouldn't want it any other way. I've let her know that we all love and care for her, that she can always speak up and express herself, that we'll move forward at her pace (no faster), that she can have her own space when she needs it, and that she can/should express anything else she needs in the relationship.
We'll continue to proceed with caution, and I'm hopeful that this will be a lifetime polyfid vee. Yes, even in a poly relationship, I'm a romantic and highly committed/devoted. ;-) Thank you again for all of your support... I really feel all the caring and support from this group to help make our new family succeed!