Thank you for your feedback and calling it 'pretty'!
I think there's two options why your character 'just sits there doing nothing':
A. He's tired and wants to sit for a while (probably not);
B. You didn't tell him what to do.
I can help you with the B option. Press 'Enter', choose a toy, press 'Space bar' and see what options the toy has. But masturbation mode was originally designed for web-camming. However, since it wasn't ready to go for the latest update, it's not there, but the 'masturbation' mode is.
So i wouldn't actually use 'masturbation mode' for upgrading your character's sex stats and progress further. Instead go hook up with your landlord dude and have sex with him. He can destroy your character's anus and throat, and you'll progress (your character will progress).
I know, it's my bad that there's a lack of tutorial. The 'game' does have some interactivity. This whole 'Sissymaker' mode was designed to test the progression system.
I'm sure you are not stupid, and i'm 100% sure that the game is not just an 850mb screensaver (wouldn't use it as one).