He apparently kept saying "he's coming for me" (in the novel)

My understanding of this is:
With all the rumors circulating of "Douglas Ford - the strongest guardian adventurer", it's clear that Douglas has recovered his strength.
If Douglas recovered his strength, that means the curse was broken.
If the curse was broken, the ring was found.
If the ring was found, Douglas knows Alan was responsible.

Alan must have become paranoid that Douglas will come take revenge, so he has gone into hiding.

(Douglas probably couldn't care about revenge - He only cares about Ravi now; but Alan doesn't know that.)
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Hito wo norowaba ana futatsu
_{“Curses, like chickens, come home to roost.”
“He that diggeth a pit shall fall into it.”
etc.}
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It rebounds upon the caster or whoever benefitted from it. I don't know exactly if the hero cast it, but he's definitely related to it.