You probably could have – would have – saved him. You probably were one of the few people who ever had that option, not that you ever knew you needed to take it. It was your fault and you kind of know that; people keep telling you it wasn't, but what the fuck do they know?
You treated him like shit and you know it. It just never occurred to you that it was the wrong why to act; he was the Beav, he was your dorky little brother, making fun of him was all part of the job. Yeah, you took it too far sometimes, but that was just what you did and one of the things about Beaver was that he pretty much always forgave his big brother.
Actually, given you're not dead yet, that's probably true.
Maybe, if you had acted differently, he could have said something. Maybe if you hadn't locked him in the cupboards for hours, or held him down and let a spider crawl over him, or ripped the shit out of him whenever he was trying to have a conversation, hadn't given him a nickname that was slang for vagina; then just maybe he would have been able to explain to you what was going on. There were too many variables and somehow he picked the worst ones, and now Beaver – Cassidy, his name was Cassidy – is dead and it over. Pooft. Kaput. No more Cassidy-Beaver.
You're kind of pissed at Beaver for blowing up that plane. You're kind of pissed at him for a lot of things, but you really wish you had the opportunity to kill Goodman yourself. That was the son of a bitch that broke your brother for good. Having a distinct villain still alive to kill would be useful, but the Beav couldn't even leave that for you. You kind of know it was his battle, not yours, but he's the nutcase who killed twelve innocent people, of which... how many? Four? Were at all relevant, so he doesn't get to decide what is the best revenge plan. Or didn't, because, you know, dead.
Some part of you knows it's not that simple; that most kids who have something like that happen to them (you still can't bare to put it into words) don't wind up psycho like Cassidy did. Those are the bits that make you feel guilty. You know the way you and your dad treated him, probably was what rendered him beyond saving. You made him a punching-bag, and then your eyes slid right past him – like he was going to tell you his secret, give you ammunition to belittle him further.
You miss him. You never really felt that feeling before; your parents were always distant and uncaring, so when they ran out (both of them) you didn't care that much. But Cassidy... it was the Beav. Your little brother. Pretty much the only person you ever asked to stay there, stay consistent for you. But he couldn't manage it, so he killed a whole bunch of people (including that chick you were banging, thanks for that) and threw himself off the roof of the tallest building in town. And you had cried. Broke down in big fucking girly tears because he was just dead and there was no undoing that.
And of course, the best way to numb the pain of your little brother committing suicide, was to find out he was a deranged mass-murderer due to the child trauma you never even fucking noticed, right after. Like if you broke your arm and it's killing you, you bring someone in to cut the damn thing off.
You can't say it was just what Woody did to him. You can't say it was you and your dad and they way you acted either. It was a lot of things, a whole fuckload of people who pushed Beaver (and a whole bus full of your classmates, more literally) toward the edge. So you grieve. You cry and rage and ask yourself why you didn't save him; why you couldn't save him?
You ignore that tiny voice at the back of your head; the helpless, paranoid one. It tells you he couldn't be saved. That it wasn't you or Dad or that perverted bastard that made him so broken – maybe, deep down, it was just him.