the answer for ur example is "부터" I've been wanting to go to Korea since I was a university student. 대학생 때부터 한국에 가고 싶다. (I want to go to Korea since I was university student) other example.. 어제부터 눈이 많이 와요. It snows a lot since yesterday.

I think I learned this before even though my Hangul is only at beginner lever but the words for since in Hangul is 이래 - ilae but I'm not too sure how to write in paragraph

왜냐하면 때문에 ...