Jenny, My personal feeling is that your reached a state of differentiation that you were able to maintain in the presence of your H's bluff. I don't think he really thought you would move forward with D; you would re-fuse like so many times before and then repeat the negative pattern. I also think that my failure to separate from my H came from both of us realizing that we somehow are forever enmeshed with each other and that we had better turn things around if this was going to be our life.
It's like I am choosing fusion, but I know it's my choice, so it's less fused than I was before. You chose differentiation.