Mortality rears its morbid head once again, I see.
Now, since I'm not a very sociable person, I can't say I've lived through an event such as this one. Thus, I can't claim to know what you're going through, Dac. But for what it's worth, you have my sympathy.
I can, however, perhaps offer some insight into the method behind his madness. Of course, I'm no expert in this field and I have no personal experience with such macabre thoughts, but I've learned quite a few things about the human mind and how it works over the years.
You say he was a very sociable, happy-go-lucky sort, yes? I don't know the specifics of this case, of course, but I've often found that people of this sort hide much behind the smiling façade. They often tend to be quite vulnerable to emotional impacts as well. Perhaps his aunt's death sent him into a much deeper depression than it outwardly appeared. That's the problem with extroverts. You think you've got them all figured out because you've talked with them at length and believe they have nothing to hide since they're so open about most things. Unfortunately, looks are always deceiving.
Take me, for example. I'm an introvert, and I imagine most people think me a cold, callous type who doesn't want anything to do with civilization at large. They'd be right to an extent, of course. I'd rather just sit here and be myself rather than go outside and either wear a socially acceptable mask or be judged for my quirks. But that's only half the story. While I've grown used to solitude, I do get quite lonely at times, especially since basically the only person I ever talk to is serving his stint in the armed forces at the moment. You could argue that I should just make some new friends. Trouble is, I just don't know how, and my general demeanor makes for a rather poor first impression. The fact that my circle of interests is rather exotic doesn't help much either.
An extrovert has the inverse problem. They know how to play the social game, but when it comes to their own emotions, they tend to be rather clumsy in working through them. They'll either lash out at their friends or keep it to themselves and let the negative thoughts fester in the dark recesses of their mind, growing until they become all-consuming. Since they've worn their social mask for so long they often forget who they are under it, and when circumstances rip their constructed identity away from them, they'll find what lurks beneath it to be strange, alien, and yet somehow familiar. Which just makes it all the more horrifying.
The death of someone close often forces people to stop and think, as you are doing now. His aunt's death most likely caused him to do the same, and being an extrovert, he probably just became excessively confused and frightened when he had to confront his own grief. Unfortunately, people rarely react reasonably or rationally in such a state.
As for how to work through this yourself, people have already been offering plenty of hugs. That's the ticket, right there. Go hug something. I don't care what it is, just find something soft and warm and squeeze it tightly. The feeling of closeness will either calm the emotional turmoil or force it out of your system, allowing you to think more clearly. Should be easier sailing from there.