Well humans love the number two. Things are black and white, right and wrong, liberal and conservative, light or dark, male or female. It's easy, you call something one thing or the other, or, if its not one, it must be the other by default.
Nature, the world, and the universe seems to be a bit more complex however. In reality things exist in ranges, from here to there, tertiary and primary and shades in between. At the very least things must be at least a box with an x and y axis, and not just a straight line, a to b. Political views don't fall an easy 'right' and 'left' line but also exist in a range of the almost never talked about y axis of political thought, the one between authoritarian and libertarian. In any deeper, and truer notion, it's much more of a sphere with co-ordinates plotted in three dimensions.
Take sex. Gay or Straight? Is that the only choices? Of course not. Everyone knows that in fact most sex is what? Yup, its not with either, its with the shower head, pillow, hand, blanket - whatever. It's not gay/straight, because there is no one else there to gender it. Now, if I assume that in fact most sex, for most people, is masturbatory, then the whole gay/straight deal doesn't apply to the majority cases of this behavior/action - most sex is not gay or straight. Yet we persist, like its the only thing in all of it that matters, or that we can get our head around. Again, sexuality and sexual choice exist on a hella lot of axis that are not about the gender of the partner. That's one thing, but its not the only thing. The reality is much, much deeper, and more complex than that.
So you, and many other people in here, are not in any strict sense crossing over the border and living on the other side, but its far more like playing on the periphery, funnin' on the frontier and pushing/stretching stuff that had been pretty rigid up to this point. Out past the perimeter there are no simple definitions anymore. It's no longer a strict one or the other.
And I think that most of these words like 'transexual' are so messed up that it's almost impossible to arrive at a simple, all inclusive definition that everyone here agrees with even here, and outside the community the term is used in so many ways that's its become less than helpful. Though I don't think that self-defining yourself to other people as a 'non' anything is of much use either.