Ok, so I've given it some thought and I've decided that I actually have multiple issues with the way that the willpower check to resist lewd actions currently work.
The first is that it appears that the difficulty is always the same: willpower < lewdness + sensitivity + fetish. This doesn't really make sense, because it ought to be easier to resist having sex with a stranger in public than to resist pretending to be someone's girlfriend. A simple way to address this might be to have the check only look at lewdness beyond the minimum lewdness for the action.
The second is that it is far too lenient. I have to ask what kind of player/playthrough is the mechanic meant for. I would say that someone doing a high lewdness run is going to seek out lewd scenes anyway, so the mechanic is not very important for them, it should be a challenge for someone trying to do a low lewdness run to overcome. But currently it presents no obstacle at all. With 10 lewdness, 5 sensitivity and 5 fetish, which is a lot, especially for a low lewdness run, but even then you would need willpower to be less than 20 to be forced into the action, which is extremely low. I would suggest tying it to difficulty, each point increasing the minimum willpower by 1 on easy, by 2 on normal and by 5 on hard. If not combined with my first suggestion, or something like it, then 5 on hard might be a bit much, maybe drop it down to 3 in that case.
And finally the game very rarely forces you to engage in conversations where a lewd option is offered, so it generally doesn't matter how the willpower works out because you can simply choose not to engage in the scene. The only cases I can think of off the top of my head are John asking for alternative payment for teaching protect, peeking in the shed in the refugee camp, saving the slave girl in the festival and talking to the bandits on the bridge. The demon cultist prisoner in the jail in Trademond has to be talked to, but Aura doesn't need to answer his request unless you talk to him again for instance.