The author has not ignored them. Most chapters in the last few years have a part A focusing on Jian Yi/XiXi and a part B focusing on He Tian/Momo... What happens is that Jian Yi's parts usually are most humorous (silly boys being boys) or nostalgic (lots of childhood memories)... That has always been a big part of Jian Yi's and Zhan Zeng Xi, because they are childhood friends. He Tian and Mo Guan Shan have more of a serious heavy aura because He Tian IS INTENSE and mysterious by nature. It is very possible the author is not "advansing" Jian Yi/Xi Xi's romantic relationship fast because if she does, the resolution would be too fast, there would be no conflict... Because they are best friends, they already have a bond of loyalty, trust, understanding, etc. He Tian/Momo's relationship needed way more developement because they didn't have that: they didn't trust anyone, they didn't know each other their entire lives like the other two.