Okay, I was saying a few chapters earlier how her hatred towards the MMC and her son made no sense, and was even hypocritical, but with the added context of actually being in the house and seeing her mother being whittled away, the mocking and belittling indifference of the duchess, and the fact that the MMC as a child tried to hide what was happening (as children do), it makes far more sense why the MC would hate her husband, and not want to be in the house.
There's a world of difference seeing you're mother dying, and only hearing of her death.
Still, it's kind of absurd that the MMC forced her into the marriage then, and that he didn't trying building a new house or something - given his love for her.