A quick explanation of what's currently going on in Malade for everyone who's too confused because I feel like I own you all this XD

Let's star from the present:

Su Jin has dreams with her future self in them. She discovers that she needs to save someone close to her who's going to die (how and when is still unknown). Because of the hints she's got - a guy, with blond hair, owning a t-shirt with wolf on it - it's most likely Baekhyun). There's also a mention about a train so that 'dead' can be an accident of a suicide. At first she got to see a monster instead of her future self. It was before the door between present and past were open and Su Jin from future couldn't connect with her present self in a proper way and send the important message.

The door between future and past can be open only for people who went through clinical death (their heart stopped beating). Su Jin didn't have any life treatening accidents so her future self couldn't connect with her. That's why they used Sehun, who in age 16 went through a big accident and almost died. For him the door is already open. So Sehun from present has the meeting in his dreams with his future self who warns you about everything and convinces to 'kill' Su Jin.

As you can see already, Su Jin from the future needs Sehun's help to time travel. Let's move to the future then. 30 years old Su Jin asks 30 years old Sehun to help her. He has to go to his past in his dream to convince his young self to open the door for Su Jin. To do it, he has to fall asleep and time travel to past but since time traveling is dangerous and staying in the past for too long will couse a coma, old Su Jin doesn't let him do it without supervision. Since olny they know about time travel, Sehun has to sleep in a place where Su Jin can wake him up on time. But Sehun is already married. So he lies to his wife he's going to a party and instead goes to Su Jin's house to spend a night there. Twice. His wife discovers that Sehun was in Su Jin's house and that's why she hates her, thinking they both have an affair.

So let's go back to present now. Sehun's and Su Jin's information about future are different. She knows she has to save someone with blond hair and so on, whose life she destroyed. She probably did something that pushed the guy to commit suicide or just didn't save him from an accident on time and regretted it in the future, not able to live with the blame. On the other hand, Sehun knows that it's actually Su Jin who's going to die. How is it possible? Maybe Sehun from the future knows that Su Jin won't be able to accept the fact she could've saved the guy but didn't and at the end ended her life as well. That's one of the possibility. They both have to find out the truth.

This is how it looks like for now. Any question?