Nanook seems like a truly special dog. I know that you have had him since you were young, and I know how hard it is to watch him getting old.
Last year I lost my 17 year old cat I had had since I was in kindergarten, and it was so hard to let her go. I sincerely hope that however long Nanook may have left is cherished by both of you. Sometimes we don't get to say goodbye, but you have that opportunity and I'm sure your last months with him will be very special. I'll be thinking of you both.