Hi dianab,
You are right to be concerned about long term complications associated with diabetes. The good news is that they are by no means inevitable, and actually completely avoidable if blood glucose is controlled within a normal range. There are a number of long term T1s on the forum, including me, who have no complications at all.
As for scuba diving and his furure career, I got my PADI license 7 years ago (joy!) and diabetes has never been an issue. Careers guidance might be able to give useful advice about possible restrictions relating to deep water stuff?
All the best,
fergus