The situation with your brother sounds awful and I hope he gets the help he needs to sort it all out.
One word of caution though- no-one ever really knows what goes on in a M apart from the two people who are M'd, ( and even then they don't always see the whole picture). Maybe there are things going on that your brother is not being truthful to you about or things he doesn't want to discuss. There may be a very good reason he is behaving as he is.
Just be a comfort for him; someone for him to be able to talk to and unburden to.
Saffie me 46 H 46 M in 1986 D20,D18,S16,D13 H's A 01/05 to 07/06 H recommitted to M 07/06 renewed vows 09/06 Going from strength to strength