Her ex was the one who did it. I'm not sure how but she's the owner of the debt, I'm assuming she took it for him.
He got into debt to pay for her medical treatment / operation after she got a miscarriage. Reason why she feels responsible to pay it back. BOTH are paying it.
Her ex is trash but he is paying it too. The reason he's staying with the other woman is not just to for a quick f*ck but also to freeload. The ex is not swimming in money still example him not being able or bother to rent a house for himself, afford car etc.
Oh yeah. This assumption and idk if in korea banks operate the same way. But usually if one has a debt wuth late paryment history under their name + low income in mind, it is less likely that the bank will loan them more if they think the person can't pay it. So my theory is that the ex already asked the bank for money to buy their basement house which is under his name if I'm not wrong. Thus when he needed money to pay for her medical bills they both agree to put in other her name. Which explain a bit why she doesn't hate him for getting both of them in debt.
Her husband did it in her name because they were married then they divorced so they wouldn't both be in debt. She has the debt and he's "helping" to pay it off
Question is this debt she and her ex accumulated together?