I wanna know what changed cause WTH he was literally so sweet to her

I think the changes happens on the early chapters aka chap1 or above, Because if i remember, our fl had a miscarriage and then ml went gambling, i think the gambling part was where he wanted to like, succeed and had a better life with her, but just using my past reading

Poverty and insecurities can beat you down and make you despise things that used to be romantic but now tires you. No grand explanation, their lives were just messy.