I reread it and in ch. 45 Zheng Xi asks Jian Yi about his disappearance in high school. So in the present Zheng Xi has his own apartment and is already going to university (I guess?). From ch. 51 onwards it’s the flashback we’re currently seeing, which is made clear in ch. 161, when Jian Yi tells Zheng Xi they need to stay together in high school too. Really need to pay attention while reading or you‘ll miss important facts and get lost.
I reread it and in ch. 45 Zheng Xi asks Jian Yi about his disappearance in high school. So in the present Zheng Xi has his own apartment and is already going to university (I guess?). From ch. 51 onwards it’s the flashback we’re currently seeing, which is made clear in ch. 161, when Jian Yi tells Zheng Xi they need to stay together in high school too. Really need to pay attention while reading or you‘ll miss important facts and get lost.