Responses
I made a post here for the first couple’s ML, and I’m not sure if he slept with others or not but it does seem like he slept with Hong Lian and omg it was more worse in novel:
https://www.mangago.me/home/mangatopic/20355717/
And for the 2nd couple’s ML, he didn’t sleep with anyone else besides MC?

I don’t remember much of reading this, I only remember hating the male leads. Did both of the male leads in both couple (the father in first part and son in second part) cheat on the main character(s)?
I get that it wasn’t a marriage out of love at first, but still. It is absolutely cruel and I detest cheaters with all my heart, fooling around and showing no respect.
Also wasn’t Hong Lian in a sexual relationship with the first ML? Any detailed spoilers about that, just so I remember what went between them. And I’d like to know anything else regarding the cheating + ML’s relationships with others.
Did the ML in first part (with Shen Yu) sleep around with concubines? Did he truly not love Shen Yu until later?
Also, for their son, I remember he fooled around with some blonde foreign prince. Did they truly have sex or was it just to make the poor main character jealous/insecure?