She need to protect him until she can take out the evil bone. If TTJ die before that, the demon god will born.
what @Kaseh Esmiralda said, she has to keep him alive until she finds a way to find and destroy the evil bone he is already on the path to being evil (forgot the exact episode where it's shown explicitly to viewers)
Right she didn't deserve to be in the human world, but she's xi vu's sister and a selfish person again
btw tian huan and bingcang are two different people, not related at all what is seen in the dream arc is ming ye's memories/what already happened its like the main leads are in a video game but puppets (can't do anything to change anything/forced to go through the whole thing) though, it will affect them once they are out of the dream
as her name is bingchang not bingcheng
it was stated in the eps that the dragon was ming ye, he created the dream thing which the characters are put into
xiao se and sikong qianluo
fairy rui and tang lian
li hanyi and zhao yuzhen
lei wujie and ye ruoyi
https://www.youtube.com/playlist?list=PLHal96yJvQA-auvL19pbPaBbn-RoiJaQ6
he is already on the path to being evil (forgot the exact episode where it's shown explicitly to viewers)
what is seen in the dream arc is ming ye's memories/what already happened
its like the main leads are in a video game but puppets (can't do anything to change anything/forced to go through the whole thing)
though, it will affect them once they are out of the dream