
I think he worked hard to save up money to pay for his college. And worked hard in school to try and pass college entrance exams. But when he saw haesoo getting abused by her dad he used that money to get them an apartment and missed the entrance exams to work or see her etc.
So haesoo blames herself for mincheol throwing away his shot at going to college and getting a good job etc.

There was a rich girl after Mincheol, if he dated her he could've gotten lots of money. He was also very smart and had great qualifications, could've gotten into the best universities but gave all that up cause he rented that place to save Haesoo from her abusive household. The guy that said Haesoo ruined Mincheol obviously wanted to fuck her, Mincheol got in his way and he spilled the tea, but all I just said was shown to us in the last chapters. Mincheol worked very hard, studied his brain off but ended up going to a regular university cause he used the money he had saved up to rent that place and save Haesoo, and he could've dated a rich girl too.
What future did Na Haesoo “ruin” for Mincheol? I honestly don’t get what that guy was saying.