I bought the game a few months ago, played a little bit and then stopped for a while. Just decided I wanted to play the game again for a bit but the new update won't download, and it is asking me to purchase the game. Do I have to re-purchase the game again for each update or is something wrong? (I have not been keeping up with updates so if an update came out were people had to re-buy the game I wouldn't know)

You just need to be logged into itch.io with the same account you bought the game with.  You can go here and enter your email in the "Recover Purchases" field if you need your game download pages resent to you: https://itch.io/support

If you download the itch.io desktop client, it'll also handle all game updates for you automatically (like Steam).

Also thanks for checking out the game again :)