What should I do when I know my autistic brother is suffering but declines any support?

My younger brother is autistic.  I suspected for a while that he is not okay.

He come over to my house yesterday and when I asked if he was okay, he said he was not, and then proceeded to say, "not that I will do it, but did you know that X amount of autistic people commit suicide?", he then went on to say that he didn't want to share what was happening because I wouldn't be able to help and he was "fine/not fine".  When I said that I would just listen to him to learn what was happening, and not offer any help, he declined once more because he said it would make things worse.

I know he's not sleeping well.

I am certain he needs support.

But I feel like ever offer seems to be declined immediately.  

There must something, or someone, that can help him and I wondered if any one could offer some advice?

I'm worried about him.

Thanks in advance for any replies!