Encountered a bug:
Upon the first weekend (or any weekend if you just ignore bonding with your step-sis), if you are in the step-sisters room and intimacy isn't high enough when time ticks over to 20:00, you get stuck in an infinite loop of the "This is a girls only sleep-over!" cut scene as the game doesn't forcefully eject you from her room. It drops you back into the last scene you were in, her room, before time ticked over and traps you.
Luckily, it's not a complete softlock as if you go into automatic saves (Or if you just have a recent save prior that you created yourself), you can just pick the most recent option prior to entering the room and not have to deal with it.