All releases will eventually be free, what you would be paying for is early access to any current non-public updates. On Patreon & Subscribestar the first week currently costs $10, the second week $5 and a week after the $5 it will come out publicly. Here on Itch it costs +$2 because patrons get better prices.
So yes, to answer your question, you would have to pay again for a future update. But that's only if you want early access or to support me/give me a tip. Otherwise, you can just wait till the public release.