Hey Uriel, if I can give some suggestions that may help you figure out your down/sex system...
I think your best option is to use Lust kinda like a "guard". When the Chibi reaches 100% lust, sex will begin and the monster will start dealing damage. Upon reaching climax, Lust reduces by 100% (but with consequences). Ideally, if Chibi doesn't resist, the monster will want to reach 100% lust before starting sex.
>Resisting the enemy allows you to escape the hold, but you do not lose your built up lust like you would by giving up.
>Allowing the enemy to have their way with you causes your minimum lust to raise by 25% temporarily, up to 75% (after being lewded 3 times). This means that escaping becomes much more difficult with each successive submission.
>Choosing to charm the enemy causes the sex to start once the charm bar fills, regardless of your current lust. This means that sex will build lust instead of damaging health, until lust is capped, which point you'll take health damage. Charming an enemy will reduce your minimum lust by 25%, until you reach 0/100 once again - and resets your current lust to 0. The problem is that the higher your lust is, the harder it is to charm an enemy - making it even harder to reduce it. So it kinda encourages players to charm more often, especially when they've submitted two or more times. This also makes charming an enemy a viable way to "sedate" them.
>Each time your minimum lust increases, your sex damage taken increases by 33%. Example: A slime could, normally, deal 15 will damage. After losing once to the slime, your next submission (which will be faster) will deal 20 damage. The one after that would be 25, and each subsequent submission would deal 30 damage (double the base damage).
>Masturbating will allow you to recover health by reaching 100/100 lust. You will restore all health, but gain 25% minimum lust, and reset your lust to the new minimum (25 >50 > 75). This works well with the gases pumping around the wolf dash area; it gives a clear consequence for building lust (reaching 100% will immediately start the masturbation animation) and also makes the wolves much more dangerous (as they can interrupt the masturbation animation and lock you into sex).
>Defeating an enemy can also drop your minimum lust by 5, then can be upgraded twice up to 15. This gives the Chibi a way to self heal through masturbation/combat, as I believe the plot of the game is "all the monsters escaped their cages, the air is heavy with pheromones, and you're fighting off the urge to have sex constantly". This would work really well as a canonical explanation on how the Chibi keeps her will up, even when dealing with all of this.
Finally, this allows you to control the difficulty of the game immensely. Easy difficulty sets the minimum lust gained to 20. Normal is 25. Hard is 30. This means that submitting in hard mode, after 3 losses, will give you 90 minimum lust - making it impossible to charm and break away from enemies. Finally, the damage increase per level of minimum lust is 0% in easy, 33% in normal, and 50% in hard (250% base damage from sex).
With this new system, you could also add a perk tree system that allows you to choose simple things like "+10 maximum lust, or +5 lust reduction on sedation, or +25% faster escapes". Each has large impacts on how the Chibi plays and how the player uses her, from survival, sustain, and control. These perk points can be rewarded on defeating a boss, finding hidden chests, or completing certain challenges, and it could invite them to explore more of the game.
If you need help with ideas, you can always ask the community. I know you're not too sure how you want the lust system to work, but I think all of the parts should work together in a way that matters. Health is "how far away from game over you are", Lust is "how well you resist sex", and minimum lust is "how horny you are from giving in to the monsters" in my concept. In the end, it's your game.