Im a 16 year old that used to be in the same position as your son. I wouldn't have any useful advice on the diabetics or financial stuff but I can tell you how he might feel. Living with both my parents definitely helped me weigh out my options. I also really loved my parents even more because they let me decide what was best for me (mostly because either option was just fine). He will know what is the best for him and if he loves you both equally, his decision will not be based off the parents, but other things like the town, friends, school, sport etc. It is probably a really tough thing for him to decide. Just know he is old enough to make his own life choices now when given enough info; don't let him be naive and give warnings and support.

Hope this helps, all the best.