I think they removed the demo, as they want people to buy the game. (I have no idea on that really, so dont quote me on that)
But to buy it you need to do so on their Patreon site, since the game got delisted from the store page due to Collective Shout that pushed the payment processors to ban adult games, just because Collective Shout wanted to get rid of one game on Steam.
The only way for the game to be seen again on the store page, was that they had to remove payment and donation from the game on Itch. Which is why you can only buy it on Patreon.