There is a page missing for this chapter where he answered the first riddle and received the second riddle I found the page but won't post it as I'm not sure I have authority to do so but you van read the raw version on Rawkuma and translate it from there with Google.
So basically because Shiori couldn't handle the effects of puberty around her and Jirou's will to protect her they both ending up deading the possibility of a relationship forming. Shiori with her extreme complex about the changing of her body and the attraction of males and Jirou trying to...