. . . we'd have to put it in the combat log or some other log . . .
I disagree with you there. In my mind, the best way to handle sex would be to handle it with just about the same amount of detail as we currently handle
eating. We don't get a blow-by-blow account of how Bomrek's tongue slams the plump helmet roast against his lower right back tooth, we just see his ☺ icon sharing a tile with the food's % icon, and his current action of "Eat". Why can't Bomrek and his spouse similarly just go to bed, where we see the rotation of tiles ☺ / ☻ / ♥, and their current action of "Sex"? We shouldn't need a damn thing more than that.
As for Adventure mode, just follow the same protocol. Do you want to eat that piece of jaguar meat you've been carrying around? Yes. Is the jaguar meat still edible? Yes. Okay then, you just ate it.
Do you want to have sex with this individual? Yes. Is the individual receptive to your advances? Yes. Okay then, you just had sex. No lengthy, fap-worthy descriptions required.
It's the (quite literal) perversion of forcing the very descriptive combat system to write violence-porn that is the obvious elephant in the room. Now, Toady could theoretically write in a way for the game to discern
sexual violence, and, if it's detected, buff the intended rape victim to be nigh-invincible . . . but that feels incredibly fake to me, especially in a game designed for realism. A more palatable (and far simpler) alternative would be to lock out sexual arousal while the player is engaged in combat. You can slam your pelvis into your victim's pelvis all you damn want, but if your genitals never get the message, all that you'll experience is frustration. Which is exactly what any would-be rapist player
should get (well, that and an in-game reputation as an attempted rapist).