Responses

Tho he started to cheat even before that. One time he was supposed to have sex with a woman who came to his office but Zishu called. Then he abstained cheating for a while but got on it again. Then for the past 3 years, Chen remained to be the other guy, as he even thought he was the only one until their first valentines.
You can reat it in Assistant Song's letter. https://www.vodtw.la/html/book/52/52551/Index.html
(might be spoiler)
The reason seme cheat on him is so disgusting..just because zishu cant satisfy him because of special constitution he go cheat like that and try to put all the blame to zishu (like damn if you know he cant stand being hurt a little why dont let him top?)
Like bitch, the first time he cheated and he got some nerve to dissapointed because zishu didnt seems like care or anger ( you fcking live with him for damn decade and you still didnt know his personality)
And at the chapters .30(?) when zishu say he know about everything he still say if he act like nothing happened ,zhisu will forgive him and he will turn a new leaf ,
What second chance, in that damn 3 years everyday is a chance but he just waste it like that,and after zishu died , he want to live for 3 years alone and after that he will suicide so he can know what zishu feels (lmaoo please dont compare yourself with him) even after all that he still only think about himself and keep asking forgiveness so he can at least feel better (XD root in hell bitch)