i already bought this game. do i have to buy it again on steam?
No need, you will receive updates normally at Itch, which will happen simultaneously with the Steam version.
The 2 versions are equal in content, however the Steam version has some features specific to Steam, such as achievements that count towards your Steam score, the possibility of playing on the Steam Deck and the possibility of playing using a gamepad.
If you're a early buyer, please follow this tutorial:
https://masturbar.itch.io/living-in-a-brothel/devlog/519670/itchio-has-banned-us...
We had some problems with Itch and they forbidden us from receiving payments here, so we had to separate the paid version from the public version and created another page for that.