At first I was also confused of the storyline. That's why I have to actually watch the movie again. Based on my understanding of the movie, the wine scene was where the husband was narrating his written novel that was also his own story, story of infidelity to his wife, Junha. He narrated his novel to his wife before he died. So when he and Naru, the mistress got into accident, he expected it to happen. It's his own orchestration. He orchestrate his death. He chose to die in a car having sex with Naru than in pain due to his liver problem. That's the starting point of the story. Naru living with Junha to atone her wrongdoing with the ghost Jane is part of Jane's novel. The lake scenes is part of the novel too. So, Jane knew all along that Naru is in love with Junha that's why he loathe Naru. The sex at the last part of the movie is an explanation why Jane cheated on Junha. The S&M relationship Jane plays with
Junha is different with Naru. With Junha, she assumes the role of submissive partner while with Naru, he is the dominant partner. The sex between Junha and Naru followed simultaneously by sex of Junha and Jane AND Naru and Jane is a dream or thought processing of Junha according to the novel. When she woke up she told the ghost Jane that he can leave which signals the letting
go process. Near the end of the movie, Junha is reading Jane's notes about his novel. It says Junha says Jane appears on her dream and that he keeps telling her she has to understand what happened. Junha is finally putting aside her husband's memento including the ring. The ending is an open ending where the real Naru with bruises appeared on the door
steps asking Junha to let her in. She brought a plant too.
I repeat everything with ghost Jane and Naru in one house is the story included in Jane's novel.