Berylia suddenly changed 180° and Redross suddenly fell in love with her. There's almost no hitch, just him being helplessly in love with her while she kept on denying reality and wanted a divorce in 1 year. Pretty cliche.

So what happend was: the author of the story transmigrated in the body of the villianess, in the middle of spending the night with the og ml, her husband.

IN the original story she is using the ML for her own gains and mistreated him since childhood smth. like that and forced him in a marriage w/her

The next morning she wakes up and notices that she reincarneted in the story she wrote, as the villianess.

Everything was fine till then but suddenly the she is saying:

, , I am sorry for everything I´ve done. I am now a diffrent person and I know u hate me, so I`m leaving.

(like she is a diffrent person but how would the ML know? like how is she supposed to turn in a diffrent person in a single night yk)

And now the ML is also like

, , suddenly I find her attractive, her eyes became so clear-the greed that could me seen in them before is now gone..." and sh*t like that.

So this story is already complety unrealistic and I´m not staying for the smut of a story that makes no sense.

He married the original Berlin knowing exactly what she was like and what he was getting into. This marriage was a very clear financial transaction made to resolve the debts of the previous generation. He was reluctant to marry this unscrupulous woman and slightly angered by her attitude when she seduces him with ulterior motives after their wedding night. You have to realize here that he is disgusted by only Berlin's personality/actions, but is overall a person who respects women. He dislikes Berlin but hasn't really opposed her to her face. She is his wife and he finds her physically attractive, so he agrees to sleep with her. He is shocked at her responsiveness during the MC's confusion due to her sudden transmigration mid s*x scene. I honestly couldn't tell if they were in the middle of it already or just at the foreplay stage at the beginning of chapter 1, but it doesn't matter much.

The important development here is Berlin's reaction the next day. This attractive woman that he despises no longer shows any interest in him and is inexplicably a lot less disgusting. He can't put his finger on what is different and does not want to admit his attraction to her, despite a hot night. This change is enough for him to become curious and curiosity is the first step toward a deeper interest. He is not in love with his wife yet in the chapters I've read, but they have started to communicate and build a bond. It's not deep enough yet which evidenced by his feeling of betrayal when he hears that she has gone off with a man through only hearsay. The point here is that he had enough trust for her to feel betrayed in the first place. It also took accounts from multiple acquaintances before he believed the gossip. What they didn't tell him was that she was bodily dragged into that room. This misunderstanding was quickly resolved and he immediately drove away the offender without any victim blaming. This entire scene from beginning to end served to display his strong protectiveness toward his wife. He defends her literally without question when it matters. He doesn't allow his friends to joke casually about her previous promiscuity.

I can't in any way imagine him falling in love with her to be a sudden change with this premise even if I haven't read the future chapters yet. Their marriage now has curiosity, communication, and trust. It's very clear that she is performing exceedingly well in her new role as his wife. She is no longer annoying and seems to be genuinely concerned about the duchy. The Duke even had an inner monologue (mocking old Berlin) that what he looks for in his spouse is someone he can work together well with. I paraphrased this a little, but Berlin treating him like a colleague fits his tastes. It's clear that future chapters will have her resolving big hidden dangers one after another. The Duke being impressed so soon may have something to do with his originally negative expectations, but it's clear that he will continue to face more happy surprises in the future. Why shouldn't he fall in love with this woman who perfectly suites his tastes and has a shared (work) passion with him? I can imagine that he is going to treat her as seriously as she treats her responsibility. His feelings will only deepen when he finds out the true reason behind the deadline. This change is inevitable with these factors.