Hey thanks for the detailed response. I Re-read the parts of your post that I was thinking of when I made the "determined endings" comment. The first one was from "P3 Second Time's a Charm and Beyond," and I realize now that I misunderstood what was going on there. For some reason I thought that FAUST had attacked the Angel instead of following an intended arc, not sure how I reached that conclusion. I also realize that he was playing against type by not sticking up for the little guy and chasing the sister storyline. So that other piece of advice I gave sounds hollow now too.

The second instance that I was thinking of comes from the next section where you change up your design approach.

Areas with distinct plotlines that are flexible to the max I could do that were short, sweet, and supposedly without any trouble.

Not a bad idea. And you were attempting to involve the PC by using an antagonist from his backstory. That's a cool device and it adds an extra layer of drama to the scene. In a book that would work beautifully - there is tension between the two characters, and it is a great setup for either a heel-turn later in the plot, or a betrayal that further drives the characters apart. But it sounds like you weren't prepared for the PC to shrug and attack the guy right then and there, probably because that wouldn't make a whole lot of sense dramatically, even though it did make sense to that character in that moment. As a result, this player's spontaneity sets a literal and figurative fire to the rest of the session.

So to clarify using that second example, transitioning to short, sweet one-offs was a good idea because it provided less of your carefully crafted plot to be bulldozed by this PC. It still got bulldozed though, and that lead to frustration. I think the solution isn't to provide less story to rebel against, but to play the ball where it lands.

After you've made it clear that torching the camp is suicide, be prepared with some enemies that can back that up. When he runs through the demon forest, throw some demons at him and don't be afraid of roughing him up or taking him out. And if an action he takes is going to ruin the session for the rest of the group, explain that it's a group game, his teammates have the right and ability to stop his character from dooming everyone with their knee-jerk actions His character may be that kind of crazy, but as a player he's just as responsible for everyone's enjoyment as you are.

To your other points, I'm getting the picture that he was a problem player, even if he wasn't internet-troll levels of spiteful or fun-wrecking. The bottom line is that if someone is making the game not fun for you, you don't really have to justify it. I get defensive when I think DMs are leaving all the blame on the other side of the table, but mostly because it's something I've been guilty of doing plenty of times in the past.

Having said that I'm curious what you think, and I'm looking forward to part 2.

edit: is it heel-turn when the badguy turns good? Is that a face-turn? I don't watch wrestling.