Nope, It's one time purchase, so you will have access to new versions.
Viewing post in Goodbye Eternity 0.6.9 available now comments
Lmao, I assume you went to the home page every time and clicked ''Buy now''? XD
https://itch.io/my-purchases - Here you can download updates for games you've already purchased.
When you click ''Buy Now'', but you've already bought the game once, you're technically just sending a donation (System is actually a bit more complicated than that, but I've decided to simplify a little.