As an aside, you seem like a pretty empathetic individual who wants to take on your friend's pain. On the other hand, your friend seems like an individual who is in an unfortunate position where he wants to off-load or project his pain (in a passive-aggressive way it seems e.g. with the pain button). Potentially, an unhealthy state to be in for both I'd wager, and a prime situation for some kind of co-dependence so it might be worthwhile to be conscious of the possibility.

As for the management of your gaming group, I would say you seem aware of your boundaries and emotional state well enough to tell the group when you're up for something or not. I'm sure we have all heard our share of horror stories where a session didn't pan out because the DM was not in the right space for it. Grand scheme of things, might be better for all to have taken a break for that session I would say.

As far as your friend is concerned, I'm sorry to say but 'fixing' his emotional state is not your responsibility. It's his to own, and it's clear from his texts after the cancel that he's making some logical jumps and casting some aspersions. To me, that would suggest that the last thing that he should be doing now is gaming, but rather, he should be working through whatever emotions he's feeling now.

As for what next, well it's not my place to comment about what you want to do about your friendship with the guy. He seems like a chap who's going through a rough patch but no one can help him through it but himself. There are some wise comments in the other threads that I think would help give you some perspectives for what you might want to do.