Brother self diagnosed aspergers

I feel weird talking about my brother, he'd hate if he knew I signed up for this. Time to delete my history lol

I'll start with this, he self diagnosed himself with his ADHD at 13, he went to CHAMS, but I'm not sure if they diagnosed him with aspergers? But he knows himself, but I trust when he says he has aspergers, you can somewhat tell if you know him.  He's also struggled with depression practically from a young age and was always considered an outcast, energetic troublemaker, the black sheep I guess, why oh why didn't we realise earlier?

At the present moment our mum has cancer stage 4 and that hit him somewhat hard, how hard I don't know. He's mildly aspergers, but as he's gotten elder it seems a bit more hard manageable, he helped me through so much stuff, was my first male role model (we hated each other up until i was about 14, he was boystorous I wanted to play shops.. at 14 that's pretty awkward :P haha) 

Anyways, his girlfriend who was good for him, left for travelling, but before she went on holiday with a rich guy, who she's done things with before, I thought she was great up until this happened, she's a horrible girl, she even said she would go for 2 years even if her mum had cancer, which pretty much sums her up.

He wanted to travel the world, do the most extreme sports, had an operation and kept jumping about, little did he know he could getand now has artharitus in his hip at 23, so the 3 combined has hit him, he says stupid things which I hope he doesn't do them. I'd say more, but It's too private for others.

I signed up for this site because I've never quite understood as it was only a later date and didn't think it was much of a problem, but he hates everything and everyone, I can't help him because everything I say he's already thought and has a negative thing put onto it,

We get in arguments he'll say horrible things and I say things, mean things which I don't mean because of all the stress. He takes what I say seriously, like he didn't mean at all, he cried in front of me when I said "I'm going to get further in life than you mate" 

I just want to know how to deal with him, what situations I should just back down, or just some advise even to take back to him, he's so smart and deserves a lot, a lot more than me, just bad luck I guess. 

I signed up to this site hoping to be able to help him, so above mildly aspergers (he doesn't throw temper tantrums and stuff, I feel bad for not know enough about aspergers when I should) I just don't want him to do something stupid, he's the best person I know, although arrogant, never wrong, and extreme hate towards people! But he has a kind heart, a brain which I wish I could have without all the bad thoughts and the most genuine person I know, so please I hope I can gather some stuff to bring back to him. I'm not as smart as him so he doesn't feel I could bring any good advise. 

If he's angry do I just walk away because he doesn't mean it? Or try calm him down, We all get severely angry, (thanks dad for the mental difficulties, me just add, my sister bipolar and a hypercondriact) 

And another quick question because it was unknown for a long time and untreated can it be harder for him to change now?

I love him dearly, but saying face to face is something we never do, he could be something, but he's so hard to deal with and speak too, blames everyone for why he is like this (which is fair) but even little things now is never his fault.

thanks guys any input would be appreciated!

Sorry for the long post :)