One thing I found interesting was how his mother confirmed to Jong Su that there was a well at Hae-Mi’s house but when he asked her family about it at the restaurant they said there was no such well and that she often lied. Jong’s mom disappeared for 16 years and only showed up to ask her son for money which you mentioned, Hae Mi also has a debt and hasn’t spoken to her family because of it I think. So Hae Mi disappearing with out a trace makes sense.

And I can only see Ben killing Hae Mi If this how he acquires his money and maintains his lifestyle. Are all the Barns he’s burned different women he’s stolen from and killed? Might be too easy of an explanation.

Also, the idea of a burning or yearning for a different life, that’s another observation I appreciate you pointing out. When Ben mentions burning barns and the pounding in his heart, what if this sparks the fire in Jong Su? He’s motivated, he’s running , he’s following Ben, he’s a detective, he has a purpose now. Ben mentions that he set fire to a barn very close, so close he didn’t even realize it. I think Ben set fire to Jong, and you’re right , after this the film is completely about Jong and his fire. He’s pretty much now blinded by his passion and convinced Ben killed Hae Mi, it doesn’t even matter if Ben did or didn’t, Jong just wants to set fire to something.

Either that or Ben is Tyler Durden.