Korean student visa date

Hi
Im currently in South Korea on a student visa D2-6. It is a 12 month visa but I’m confused as to when I have to leave to country. Here are the possible dates.

1. The date of entry which was August 21 2023 so the same date 2024.

2. The visa was issued on June 23rd 2023 and it was valid until sept 23 2023 which meant I had 3 months to enter before it became invalid. So does it maybe count from September 23 until the following year?

3. The date I received my ARC card which was sometime in sept or oct I don’t recall of the top of my head.

I’m really confused as to when I have to leave and I wanna stay here as long as I can cos of my boyfriend.

Thank you