Just not into husband's girlfriend
I think the two of them would like me to be into her, but I'm just not.
I entered this arrangement honestly, thinking, given that they had a long-term friendship with romantic overtones, there was a solid chance we would have a great three person relationship. After getting over the initial insecurities (this is our first non-monogamous attempt) and a bit of grieving of expectations, I've eased into this. It makes me happy that he loves someone else, and I don't doubt his devotion to me and our family (14 years together, 9 married, two kids, great careers, stable and healthy home life). And after spending many nights laughing and generally enjoying each other's company, I came to the conclusion that I am just not attracted to her. She is physically beautiful and very sweet, but I don't find her interesting at all (which is a must for me, romantically, sexually).
I think my conclusion bums out my husband. He's disappointed. I think he had some sort of kumbaya fantasies about how this would work out. But I can't force feelings.
She is kind of part of our family now (no, the kids have no idea that she is anything other than an aunt of sorts), so there is no drawing of strict lines. But I quite simply don't want to have sex with the two of them. They are welcome to each other alone (I still struggle with this but not much) and obviously husband and I have no intention of changing our arrangement. I like hearing about what they do, but I don't want a three-way relationship where none exists (at least to me).
What can I do to make them comfortable? I'd ask "is this normal?" but that's a dumb question. I guess what I want to know is if any of you with more experience can tell me what to keep my eyes open for, how to be careful of their feelings while respecting my own wants.