I absolutely swore to myself (most important), and three wives that I was just a cross dresser. I told myself through a good part of my life that I could switch back and forth at will, or stop. However, though I didn't know the term, I had GD, and it was progressing. I found, that like a junkie, I needed more and more, and eventually went full time (still telling myself this was a hobby!!) The GD started moving ahead at a terrible rate. I think being full time, non hormone, made things much worse, because now my mind was seeing one thing in the mirror, and feeling another. The descision that I NEEDED to transition came fast at that point. A matter of days. I knew all at once that this had to happen, or I would simply cease to exist. (I have used the 'cease to exist' phrase before, because I was way to chicken to kill myself, and way to chicken to carry on, so therefore I would have just 'ceased to exist' without explanation.)
I truly feel that most CD's will carry on, at one level or another, happily, and never need more. I think those that have GD to the point it will boil over, will know it. The rough part, you never know when that GD will manifest enough that you have to transition. Only a few years ago I would have said that once a CD, always a CD, but I disproved my own theory, I still believe the vast majority will not progress to the point of transition.