I had to blow a thick layer of dust off of my tumblr account to reply to this. I don't know if this will be relevant to anyone having discovered this so late, but I want to say I greatly appreciate this post. I have been dying to figure out what the story of this album was over the last week, and now I feel like I have a much better idea of it.
I won't get crazy in depth because I would be here all day, but there are a couple of takes that I haven't seen elsewhere:
"He hasn't been himself in quite a while"
This is the first line in Nightmare, notice how it's in third person. I believe this not just an artistic choice, but a storytelling one. I believe that this is our first indication that we are being told the story from more than one perspective, this one I will call shadow.
"Oh my dear sister Christie, I think his end might be nearing us"
That line in particular from the same song shows that there are three perspectives. Shadow is speaking, talking about the original, primary part of him, who I think of as the kid, or innocence. Notice that we only get references to Christie being his sister from Shadow's perspective. I believe that Shadow and Christie are other perspectives inside his head, or shattered parts of his psyche. It's tempting to use the term alters in reference to Dissociative Identity Disorder(DID), but I personally don't feel like I have enough of a knowledge about it to speak on it, so I'm not going to refer to them that way.
I don't think it's as simplistic as Christie is depression and Shadow is anger, they feel more like complex characters to me, and I don't have a great understanding of them yet, but I think in this context, referring to Christie as his sister makes sense, because they are both children of the kids mind.
"But gritty's kinda hard when his brain's run by committee"
I think this is more evidence that he has several voices in his head.
"My shadow, he's holding the gun with the hands that I once possessed"
This is from Christie only knows. Obviously, this is where I get the term shadow from. I believe there is a big difference between between this and the line it's calling back to. "Those steady hands I once possessed," to me sounds like the focus is on the word steady. HIS hands USED to be steady, but they're still his. "The hands that I once possessed" is focusing on the hands themselves, he no longer controls them, his shadow does.
I don't have a great understanding of what happens between the end of second thoughts and the beginning of showtime(and all of curtain call), but I think the end result is that the shadow killed the kid(his innocence.) I don't think there was a physical suicide attempt personally, I think it was a metaphorical killing of a kind, loving, and innocent part of himself. And the shadow has control now.
To not get to deep into the rest of it, I think that he's choosing to stop seeing Juanita as an ex who he loved, and start seeing her as an enemy, which is a relationship he believes he can handle better. I personally don't think Christie gets left behind forever at the end of showtime. I think that she and Shadow will always be part of the same person, and will learn to live together. Maybe he'll never listen to her again, or she will only ever have toxicity to offer, but maybe not. Who knows.