So I got 2 hypotheses:
1. Daddy's marriage has been failing for a long time and only kicked out our boi to experiment if that would change anything at all. It didn't. Daddy is gonna die alone regardless.
2. After Daddy kicked out our boi, the mother actually started hating his ass because of it. Then again, it begs the question, why did she allow it to happen in the first place? One reason could be the classic power dynamics in a Japanese marriage, aka, the wife has little say into anything. Or maybe the mother was lied to about it. I feel like this is the more likely option, because this is something interesting that the manga could elaborate on later on.