I'm going to be the wet blanket lady here.
It's good you called Barbie and that what she has been told and what you have been told check out. I'm glad you went ahead and called her and it went well.
But Barbie isn't, and never has been, the problem. I believe - and we'll never know - that if Sundance had been open with Barbie, introduced you to her, you would have wigged out. Hey, it's a very human thing to do. And then you would have adjusted, been happy for him and moved on.
I urge you to use your newfound ovaries to start talking about this whole situation with your husband. Now's the time, especially since you can perhaps check with Barbie and hold him somewhat accountable on that side of things.
P.S. If this comes across as damning or contemptuous, that is not my intent. Deity knows I've screwed up, lacked cohones in critical situations, etc.