One piece of advice I can give is try and live the diabetic life alongside your child for a week or two. Inject yourself when he does (not with insulin obviously), test blood when he does, write it in a book etc, take hypo treatment if he has too, change your diet if necessary etc, plan your day if you are taking exercise or having a lazy day and what this will mean for your sugar levels.
I know it's not real for you but that will show support and will actually give you more of an idea of what it is actually like to live with this condition. I would feel honoured if one of my family or friends would do that for me just to get an idea of what we go through each day.
You can't fix what has happened but if he sees Dad doing it and being a bit of a hero it may help him along a bit. Sending some good thoughts your way for both you and your son