Not really a spoiler since the story has told us some of these things already if you pay attention to the details given to us so far;
the story is based off the novel, in the novel the mc and ml spend their first life together but the ml treats the mc like shit and the mc has a horrible up bringing. the mc kills himself in his first life. in their second life(the present story) the ml remembers both of their past lives and is trying to give the main character a better life this time due to somethings that will be told at a later time in the story. the story has alot of overlapping memories as the mc slowly remembers his past life.
I've seen spoilers and so far they seem like a sweet couple. I wouldn't have imagined all that happened in their first life. I refuse to believe all the shit Sejin went through