Wrong in chapter 70 Jian Yi meets Xi's sister and in chapter 96 he sleeps at Xi's home but yeah you were right about the rest of the things.
what they meant was that that was the first time. he had no idea he had a sister before that
It's weird though... I think (I might be wrong) that xixi's mother acted as she knew Jian Yi from before...
She did know Jian Yi http://www.mangago.zone/read-manga/19_days/bt/311045/Ch87/3/
And maybe this is the reason why Jian Yi didn't know Xi's sister http://www.mangago.zone/read-manga/19_days/bt/f0cce9a2bba0e9ba/Ch159/pg-2/
As mention in another comment. I meant he didn't know Xixi had a sister and he hadn't stay over Xixi's house until chap 96(?). For childhood friend's, I find that really strange.
I guess what I'm trying to point out is that I feel like xixi is not someone who talk about himself and (obviously) Jian Yi doesn't want to talk about himself. Henceforth although they are truly close friends, at the same time they are not.
Seemingly they both distant away from each other; Jian Yi not wanting to say anything about his past and Xixi for apathetic nature. Althrough sometime he show a really protective emotion for his friend (which is a little contradicting.... )
I know the word "apathetic" sounds harsh but Xixi and Jian Yi are not only best friends but also childhood friend yet he doesn't even know where Jian Yi lives. Ah, I even remember when he say that he didn't even know where Jian Yi live, his face seem really shock that he didn't know (at least ow I see it).
I, myself have a childhood friend whom I know for 15 years now! We were together since I was 6 years old and I would say I know her pretty well. My parents were really strict so I was only allow to start going to her house and play after I start middle school. Since Jian Yi and Xixi seem to start being friends in an early age, I think they must've know each other for over 8 to 10 years, yet he wasn't curious about where Jian Yi lives? Somehow, I feel like Xixi is taking Jian Yi for granted, that Jian Yi would always be beside him.
After reading this chapter, I come to a sudden realization that makes me really sad.
Jian Yi and Xixi may be best friend but they know nothing about each other. Jian Yi never stays at Xixi's place. He doesn't even know that Xixi has a sister. While Xixi know almost nothing about Jian Yi's home or family, but its not Xixi's fault. Althrough Jian Yi is always by Xixi's side, he still distance himself. As if he has another side or past about him that he doesn't want anyone else to see.
I think Xixi will realize how important Jian Yi means to him after Jian Yi disappear. Right now, Xixi can't differentiate between love and friendship, his kindness for Jian Yi is just love for his friend (at least thats what it seems like right now) and that's why its painful!!
You can tell that Jian Yi harbor feelings for Xixi and some parts of him is aware that he does, but he has not come to term with his feelings yet. As for Xixi, I don't think he's dumb so I;m sure he's becoming aware of Jian Yi's feeling but (like Jian Yi) he doesn't know how to react to it
The kind Xixi that save Jian Yi from loneliness is also hurting him the most. How can Jian Yi give up on Xixi? He's completely head over heel for his friend. However, he backs away when thing get serious. His past will always be a giant wall between them. I'm sure they're feelings won't move forward until this is solve. only then will they be able to fix the situation and live happily ever after.