This is exactly how I felt when my husband and I mutually agreed to open up. We both really wanted to do it, and he only had second thoughts when I started have real feelings for someone else. I didn't want to lose him, but I'd found a way of being in the world that felt really natural to me and I couldn't turn back, even if I had stopped seeing my new love. Fortunately, my husband eventually dealt with what he realized for him was just programming and we've continued to enjoy our poly life together. Poly isn't for everyone and that's fine but for some people it's exactly the right thing, and I agree with you, that should be more socially acceptable.