I so hope that he knows that he is loved.
He does. I promise. I am not him, but of this I have absolutely no doubt. It is too apparent by the kindness, compassion and love that you share here, that you are a person who exudes love and your son has always been a fortunate recipient.
My prayer is that one day he finds recovery so he can tell you himself that even in the darkest times, he knew that he was loved.