Responses
I think in the current life, he chose to stay his whole life to take care of his sister and nephew. He could have left earlier but he didn't. That's why he said the yellow dragon is the wait who have to wait for him.
I agree. He let him live his life in the real world fully before getting him. And now they will live in yoonsuk(?) together forever without worrying of parting ever again.
This is just bittersweet. It's a fantastic story but... this ending left me more empty than happy. He wasted his life. Waiting. He had a "quiet" life, but was it a "happy" one? Did he enjoy it as it fullest? Idk.