I have this same fear in my own relationship, except I am the sub. I want to submit my power, my being completely, and in the same breath I fear losing my spirit, the very thing that is my power. For me that's what makes it the edge, makes it fresh, let's it grow. I view the relationship as being alive, yes it is part of each of us and yet it is something of it's own making too. So it needs to be tended to, reflected upon it, guided. My personal thought on the matter is that so long as I am aware of this, so long as I pay attention and give care to the matters I fear happening, they will not happen for this very reason.