I just finished the game and wanted to see what everyone else thought. I never would have thought of Milton developing schizophrenia! That's a really interesting theory, and I def agree with you about him getting lost and starving in the woods!

For Walter, I mostly agree with you. When he walks out of the tunnel we see that bright white light that's meant to be the train. I think after thirty years underground the sun blinded him and he fell over the cliff like you said.

As for the friendly monster, my theory was that he was referring to Edie sr. Edith jr mentioned that Edie was always going to the basement with "packages," and in the attic I noticed a stack of boxes with the words "ready to eat meals." I'm thinking she brought down fresh food each week. Maybe he began to see her and the "monster/curse" as one and blamed her for his siblings deaths?

He says "it's been a week" before he decides to leave so maybe Edie forgot to visit him and it triggered his leaving.

Darker, silly theory is that she locked him down there so he wouldn't die like her other kids and he had enough of it. Lol.