Hi San
I see you have made a reference to the ‘beast’ so I am hoping you have read the coping mechanism that I and many others have found helpful.
I think it is particularly good in your case where you talk of the mother/son bond – a bond that is fully exploited by a CG. 
Your health concerns me because it will appear to you that it does not affect your son and I know that, that is hard to take.   You cannot believe that he lacks all compassion.
I would have told anybody when the addiction was at its height that there was no way in a million years that my CG could love me.   It has been one of the most wonderful things about him becoming gamble-free – his empathy is greater than most.   I don’t know exactly how this can be apart from the energy and effort the CG has to go into to change their life – they become more special for the effort.   I have even heard CGs in long term recovery thank their addiction for making them the people they are.  I know the sentiment.
You can abandon/reject his addiction without abandoning or rejecting him.   His addiction will tell him differently but his addiction drastically changes his reality to fit his personal perception and you cannot win against that.  You can know you are on his side and one day he will understand but as an active addict the concept is beyond him.
There is not one member I would imagine who has not felt a pain in their heart when they have seen the tears, seen the hand wringing and heard the desperate plea for help.   How could this person not be in ‘need’ of saving and surely as the parent and therefore responsible, not be the ‘only’ person who can really understand.   Unfortunately to our cost the parent/spouse/child finds out to their own cost that they cannot save their loved one and the way to love them is not the way that comes naturally.  You are not responsible – there is nothing you could have done to prevent your son’s addiction.   To love him is stand against his addiction and not feed it.
Your attitude to living is great – to live in the present is all that we can or should worry about – what has gone has indeed gone. 
Rejection is painful and many CGs have felt rejected in their early lives but as active CGs who have ‘used’ their relatives the feeling of rejection is different.   The relative is no longer enabling and that is different to rejection.  Don’t blame relatives when they don’t understand and have protected themselves against something they fear – the addiction is the only thing responsible for the rejection – not them.  I would like to think that when your son changes they will welcome him back but I know from experience how hard this is for many – few people bother to actually learn that the addiction is an illness of the mind and not just a selfish act.  
I understand the feeling of being concerned about rejection but I think that the non-CGs feels it more keenly.
We can of course talk easier in a group and I look forward to seeing you again.   I understand completely why you don’t feel free to write everything here. 
Keep telling him where to find support and that you know enabling him is wrong.  
Speak soon