Responses
Because Geumryang, despite loving Taesun that much, he still essentially a being that adheres to nature. He didn't mess with that, which somehow a good character writing. That's why he makes that speech.
Eh I'm sure some weird magicky thing will go on or semi-doomed yaoi will happen and that's still a win for me
Rather than live long, why not live as long as Taesun hmmmm?