Comment by yuriyuri on I'm a Villainess to be Poisoned, so Why am I Being Adored? - Chapter 18

Lazy explanation

Dude basically abandoned her in a separate building, never came to see her, and never bothered to check on her condition
On top of that, if he 'had' to marry someone, that doesn't mean he needed to give her control of the house. It's your title and your house, just keep up the bare minimum with them while taking care of your kid.