Has therapy helped? I know we as type 1's face burn out. It's why I asked does he have any issues in college, among friends? I know the youngsters want to eat, drink, flirt with girls etc, like be carefree. It can be seen as form of self destructive behaviour, but ignoring diabetes won't make it go away. There are things that can help him test, like CGMs or Freestyle libre sensors, Whether that will motivate him to do better, I don't know. One can only try eh? But those tools make our lives a tad easier and comfortable, however you still need to test to calibrate from time to time. It is discreet, your son can use his phone with NFC to scan the libre sensor, his friends wouldn't know. You'll need to speak to his team or consultant to ask about it. As for insulin, I wouldn't know, other than to encourage him to take it.
My mother too, had to watch me go through DKA for the first 3 years of secondary school. We all know what happens if we don't take insulin and it is hard. DKA isn't nice and I wouldn't wish it on my worst enemy. I am sending your family and your son lots of hugs, things will get better. He needs you right now, it might be his attitude doing all the talking but there's a small part of him saying "dad, please help me".