I grew up moving between schools abroad, and I watched my Korean drift a little further away each year until I decided to hold on to it on purpose.
The trap is that school runs in English, friends speak English, and Korean quietly becomes the language you only use with your parents. Without a reason to read and write it, the vocabulary that once felt natural starts to fade.
Small habits reverse this. Read something in Korean you actually enjoy, whether a webtoon, a news column, or a novel, for ten minutes a day. Write a short message to a grandparent each week. Watch a show without the subtitles and let your ear do the work.
If you are preparing for study or a career that touches Korea, treat the language as a subject worth real time, not an afterthought. A tutor who moves easily between both languages can help you keep the fluency you already have while you build the academic side.
The goal is not perfection. It is to make sure the language that is part of who you are stays within easy reach.