
Literally this is why me and my partner decided to not get married before being together for 8-10 years and living together for a couple of years. I'm not saying those that marry early and have known each other for a year or a couple of years are destined to have an unhappy married life but, just saying there are chances people change. Plus we want to be financially stable when we do it.
I dated a guy for 1 and another couple for 2-3 years, and I can testify that people change overtime and thus I decided marriage mustn't be rushed. My partner thinks the same way. We don't want to be together for marriage obligation or worst kids in case love fade away but because of love.

The thing about this webtoon is that Mincheol and Haeson seem to have married to get her away from her family (so her parents aren't her guardians prob), pregnancy and pay her medical debts for her miscarriage. Mincheol back then seems to not think of seriously marrying her that early. Maybe sure he wanted to marry her but not anytime soon. In fact, he seems to think of going to college/uni but then to helping her get away from her abusive parents when found of the abuse. Then there was the baby that that they lost which initially made him commit for their kid well-being... Like these was his priorities.
His love for her prob twisted and became a hate-love thing because her circumstances and various event outside their controll unintentionally screwed his life (despite he consented to it and she didn't cause or want it. ), I mean seems like his family disown him and all his hardwork saving for university were instead used for her debts.
mincheol is the perfect example of why it is so scary to fall in love. he was so in love with haesoo and they loved each other so much, idk why he changed like that. i know this is just fiction but I've seen people, my closest friends go through the same thing and it's scary how much a person can change