First things first, I'm very sorry for your loss; it's never easy to lose a friend, let alone one so young. With that said...
This hit so close to home that it's scary. I'm 24, and my weight hovers between 350 and 385lbs. I've always been fat and otherwise unhealthy. While I don't eat a lot (I definitely eat more than I should, but I don't think that I eat to excess by any means), what I do eat is terrible; that's gotten worse since I moved to NYC and had money to get delivery effectively every night, meaning I eat at my computer and pay no attention to what I'm eating. In my case, it's not gaming but programming that's killing me; I don't get away from the computer and exercise effectively at all, and even if I ate perfectly I'd still be screwed for that reason.
But with that said, blaming programming/gaming/whatever for my health problems is like blaming the manufacturer of my chair for making it so damn comfortable. At the end of the day, it's an excuse to take the attention away from the real issue: sedentary lifestyles are unhealthy and will kill you.
I don't want to get too far off-topic here because this is about your friend, not me or anyone else here, but the focus really needs to be put on a healthy lifestyle, not on isolating one specific component as the failure point. A serious change in my life (and I imagine Russell's) wouldn't involve removing the object of obsession, but changing a million factors, and it's definitely easier said than done; that said, it's something I'm working hard on myself if only because... I want to live.
Edit: Something that I missed while writing this initially, as I got caught up in it.
> We should have tried harder.
I know you say that with the best of intentions, and I know that you're beating yourself up over this, but you shouldn't be. Speaking as someone who's been on the receiving end of that many times, I can't describe how deeply embarrassing it is to be in this position and how much shame is involved. I know you can't exactly hide being this fat, but you damn sure try to put it out of mind and keep it from being a topic of conversation. That absolutely makes it harder to get help. Think of it like someone being a closet alcoholic, but they always reek of beer regardless.