In addition to the reputation systems, some sort of endurance stats so that the more you have tiring/painful sex, the less tiring and painful it is, so you require less or eventually no potions just like you require no perfume later on.
Fatigue loss should be capped, like how much it takes on a Naiad should be the minimum (you can't just run around and then have sex, catch your breath first!), and actual attacks or environmental damage (ie falling) would not be reduced. At best, I'd say Flint's endurance should be capped to what that monster would hurt him too, so training on Lycans wouldn't stop Minotaurs from hurting him.
Lube as a temporary defense against painful sex would also be neat.