For Level 2 H-scenes, you usually need over 100 Lust, and for Level 3 scenes you usually need over 200 Lust.I can only get the first events from losing to the demi-monsters or whatever. How do I get the second and third events?
You reach those levels by raising your Max Lust, which is done by reaching your current Max Lust (99 or 199), going to your bed at home, masturbating, and selecting the appropriate option.
You don't have to get all of a boss's H-scenes the first time you encounter them, as they will all come back near the end of the game.