Poor chap he must pretty much feel like his whole world is falling apart and he has no control...
Not only is he grieving for his lost future (coming to terms with diabetes you go through the same emotion as you do with a lose, the same 5 stage process) and now you both grieving for your lost child... And this will impact not only the control side of his diabetes but also make it all difficult to come to terms with his diabetes..
At the moment if talking about his diabetes sets him off, then avoid it for them moment let him have some space... It may be that he just needs time to get his head around all that he needs to.. Sometimes a good intention and wanting to help can be percieved as nagging...
What you can do, is give either his GP/Surgery nurse or diabetic clinic a bell, they won't be able to directly disguss his diabetes with you as this is confidential, but you can explain what happened, what happening so they are aware for his next clinic visit and hopefully then they can get him to open up a bit and perhaps get him some counselling etc...
It's hard to take a step back when you care for somebody, but sometimes taking this step back enables that person to open up more then you are able to help them more