is there a game guide?
I don't think Hyao will update the guide from time to time. However you can ask other player or just Google the question you want to ask and if you are lucky you will get the answers from older comments in Itch. Io
Eg: Google "How to get fourth heart from Bernard in Lustful Desires" and try to go through previous comments.
*Tips: Make sure you type the keywords "In Lustful Desires"