It's funny, so often on threads where a woman has found herself abandoned for a younger, sexier, model, and left to pick up the pieces of her life and the lives of her children, she's told, "don't worry, eventually he'll realise he made a colossal mistake".
Your brother, I am afraid, is in the "shit, I made a colossal mistake" period now I guess. LIfe with his first wife was perhaps a bit boring, less sex, lots of responsoibilities to deal with the children and he didn't want that. so he went off and found excitement elsewhere and blew up lots of lives.
And now, years down the line, he's miserable and unhappy.
I am sureyou love your brother but this is HIS fault. he chose to abandon his family. If he could do it once, there's no reason he couldn't leave this woman too. He probably hasn't because he can't' find a hotter, younger model anymore and it would be to expensive anyway.