Type 1 diabetes is a relentless burden. It pushes buttons from the inside, often bypassing your natural coping mechanisms. Low blood sugar and high blood sugar both mess with your mood on a purely chemical level. On top of this, low and high blood sugars can cause feelings of guilt, frustration and anger. The management of diabetes can be exhausting. It's something you never get a break from, even when you take a holiday. It's often isolating, leaving the sufferer feeling like they can't discuss it with anyone because it's so complicated. I could go on and on.
Although it seems like a "physical" disease, and often medical professionals view it as such, it is very much a mental condition also. I went through a period where I was regularly contemplating suicide. For a long time I didn't realise I was depressed, angry, stressed, anxious. I didn't understand the feelings because a lot of them came from deep, deep within my subconscious. I couldn't understand it, let alone explain it to anyone. I think my body was just worn out, driven to an exhaustion beyond exhaustion. I took a year off and my family looked after me, and I think that was the main reason I recovered.
Type 1 diabetes has been described "like living with a baby that never stops crying". Your brother has lived with that since he was 9. I can't give you much specific advice, because his situation could be quite different. But maybe some of the things I've said will help you understand what he's going through and what he might need.
I will say one thing though: people take their lives when they don't see meaning to their suffering, and diabetes is constant suffering. Make sure your brother knows he is valued, and if he has lost meaning in his life try to help him find some. If he has no diabetic friends to turn to, maybe it would help him to come to a place like this where nearly everyone will understand his struggles.
Good luck, and I hope this has a happy ending.