So Incheol (the bottom) found out that Pyeong-hwa (the top) is the son of a woman he once tricked into giving up her property I believe (the stamp that the woman gave to him is basically something like a signature, so as long as he has that stamp he can fill legal papers in her name as much as I know) and then when Incheol met Pyeong-hwa in front of his apartment door and went inside with him he asked about Pyeong-hwa’s past. Incheol did find out some information about his past through a background check that a policeman secretely gave him, but Incheol still was curious as to why pyeong-hwa turned out the way he did and how he had been living after his mother’s death (which Incheol feels guilty of since the mom died while he was talking to her and she most probably got a shock/ heart attack from something he said or from finding out she’s being tricked).
Pyeong-hwa lived with a police officer after his parents died and that police officer sexually abused him while he was a child. Once Pyeong-hwa grew ‘too’ old the police officer lost his interest in him (disgusting pedophile).
So basically we got Pyeong-hwa’s sad backstory and we learned of his trauma. We also learn that Incheol knew Pyeong-hwa’s mother and now Incheol probably feels a little bit more emotional and sorry for Pyeong-hwa.

So uh.. I'm a bit slow in the head and a bit confused on what's happening like I know but also don't..I need someone to tell me in easy English what's happening because my first language isn't English and my vocabulary is very limited so I don't understand alot of the words..