I'm very happy to know you like the demo! Thanks for giving it a chance and taking your time to read it :D.
To answer your question, yes, you will have to purchase Act 2 separately. While Remnants of The Past has a main story, each Act features its own independent plot that intertwines with the main narrative. Although I refer to them as Acts, they are a saga of books. They are all connected and advance the main plot, but each one focuses on a specific character and tells its own distinct story.
A little edit to add: Every act will follow the same process as Act 1. I'll post the first draft for free until the last chapter, and then, the full version will be free for a week. After that, the browser version will be limited to just the first few chapters as a demo. I thought this would be a cool way to show my gratitude to everyone who decides to share this journey with me, and to give people who cannot afford it a chance to experience the full story at least once until they can save enough to buy it :D