I was just going to mention cushings, but I was beat to it.
I'm sorry you and your little dude are going through this. But like the above poster said, diabetes in dogs is very, very manageable. And the dogs can live long, healthy live once it's under control. My aunt who has had many Cairn Terriers her whole life had one with diabetes who lived until 13. And she even had a tendency to break the rules and go through the McDonalds drive thru for Devin from time to time
My last Cairn had cushings, which is a little scarier than diabetes, but she lived until almost 10.
Belly bands are amazing. They'll not stop the accidents but until you get everything under control, they'll stop your panic with the pee clean-up, and his panic from going in the house when he can't help it.
Keep us posted!