Okay. GRRM has published five volumes of the SOIAF series, the last in 2011. He started writing the first one 25 years ago, so he's not exactly cranking the books out--he's said that he's many months away from finishing the sixth book. He's also publicly projected the saga as a seven-volume series, but has painted himself into so many plot corners that it's easy to imagine that eight or nine, even ten, might be needed.
[The best parallel I can come up with is the Wheel of Time series. Robert Jordan originally planned that as a six-volume series; he died while writing the twelfth and "last" volume. He left extensive notes for completing that book...but when his successor actually started the writing, it became clear that three books, not one, would be necessary.]
GRRM is approaching 68 years of age. If you've seen the man, or pics of him, you know that he's not in shape (except in the classic sense that round is a shape). He has other writing projects going on, is involved with the plotting and production of the TV series (which has outstripped the books), and generally has become a victim of the series' success: he participates in many SOIAF-related events that take away from writing time.
So: Enjoy the TV show. Enjoy the books that GRRM *has* written (I have). And enjoy the rest of the book series, which I'm confident will be written by someone or other.
Just don't expect George R.R. Martin to be the one who finishes it.