She isn't her sister but just a " good friend ". He will not have choice. He's a simple person without title. He becomes comte thanks to MC. It's the reason why they need MC for the child. So after the divorce he will loses everything and have to pay MC. And the "good friend" loses all, she choose to be a mistress so now she is done. In chapter 19 she even tried to show up because trash husband buys clothes for her. I loves how MC take her down !
There is a novel, but it's only on Kakao. 1 chapter every 3 hours so it's not a quick process for anyone who wants to read. But so far the chapters are 1 to 1 with the manhwa so not missing much yet.
FL discoverd then one of her employee helps her husband's mistress. She makes a rumor about her pregnancy. She is not but she makes sure that the employee knows. And just after, ther mistress knows and comes to see FL. The mistress things she is pregnant with baron (ML)'s child. the husband to stop the rumor about his mother and sister, he make rumor about ML. He says he was a trash so now every one talk about that but he don't care. the count wants to make a party and he wants his mistress to be the hostess. It's really slow and i'm sure ML hides something, maybe he's more than a baron.
I think it was already hinted in the manhwa that ML is a royal prince from another kingdom and if I’m not mixing up the stories his “last name” is actually a title there. It was also hinted that ML and MC have met during their childhood. But I don’t understand yet his affiliation with the current kingdom as he’s apparently helping the king/emperor of this land with some intelligence work.