Your parents was just poor, they are working under the family of Sunghoon, and they were worried that, Sunghoon might not have a lover since he's an asexual, and when they found out that your mother have a daughter, so they decided you to be betrothed of Sunghoon when you turn 16, you're parents were worried but they just agree

Sunghoon mother: y/n pleased accept our arrangement, we just want our son to have a lover, and and you can have everything you want, just agree on it