Thanks to everyone who responded to this.
I think one of the reasons its upset me so much is that when all else fails, ie; keeping homelife calm, listening, smiling, holding him, telling the truth about the man I really see and not the one he thinks he is.. when all this fails, and sometimes it does, and this beautiful warm and intelligent man retreats into himself, I simply tell him I love him.
I recognise that this is more about me and one of MY coping mechanisms at risk.
Whilst its left me feeling a bit defeated its good to realise that if this is the case actually those three words won't be any loss to him.
On a humerous side he's been trying, without any remote success, to get me to tell him "You are my lord and master" for years. I might even indulge him just once or twice. :-) :-)
I've found something in each of the above posts, too much to quote, but thanks again for the support.