FYI: Spacebar to open the menu, including to save manually.
(Not very intuitive, though. I tried Esc, Right Click, even the F keys before I would have thought of Spacebar. I read through older comments here to find it.)
If the author would consider adding some note, at least, indicating how to access the menu in-game? If he is willing and able, perhaps change it or supplement it... Esc would be a good choice, as it is a default menu option in many games, and possibly the Right Mouse Button that people are used to in these interactive gay stories.