Spoilers in the novel

Spoiler
- The sister of Kang will know about the existence of Taeyang.
- Juheon will tell Kang sister about everything and ask her not to tell Kang about Taeyang.
- Sister promise not to tell Kang but she gives clues to Kang about Taeyang and tell Kang to invistigate again because he doesn't know who really is pregnant. ( You know his misunderstanding about the hospital scene)
- Kang will invistigate again because the words her sister tell makes sense. And when he search the sns thingy of the girl he misunderstood that is pregnant, he really doubt himself and start to feel guilty. But still he want to ask Juheon to really confirm it.