Its actually quite common in asian countries for the spouses to sleep in different rooms. And also back then it probably would seem like they were desperate or something
It Was common to get married for political reasons not for love(which is the case here).They also used to believe that sleeping in separate rooms was good for their relationship.(its not an asian thing) it was an victorian thing.
This webtoon created by a korean but the setting is obviously not in asia, so i think the reason is simply that they were not a lovable couple before the MC's soul transferred to the wife's body
If i remember correctly, the real roselia (before MC's soul took over the body) said that she doesn't want anything to do with the duke's family, so maybe that's why she's only wife by status and they got separate rooms
Sections of each reply here is correct. I love it.
Sometimes i wonder why they have a separeted bedrooms eventho they are married