Before they know it, Sherlock is just as read as Irene - i.e. not at all. Not that John knows that.
Sherlock knows, even as he jumps down the waterfall with Moriarty, that his plan is crazy, insane, and that he is the only one who would have thought of it. That is true of most of his plans. It is only pure luck that he survives, that and Mycroft (not that he'd ever let his brother know it), but the thought doesn't shake him. You get used to those kinds of odds living his kind of life. London at night is not a safe place to be.
And before he knows it he's dead - or at least to the rest of the world. Only Irene's dead for real.
Or maybe she isn't. After all one day it occurs to him that she's just as good as him and if he could manage to fool Moriarty with this then maybe she could to.
That thought is what carries him through the next three years until he sees John again, until he can live again. Until then he is merely a ghost, a figure in the back of their minds.
And maybe Irene is as well.