Well, it would be cool, a pregnancy mechanic, like the character would tell the MC that she's on her fertile day and it wouldn't be possible to have sex, then it would be a good excuse to put on condoms, this would make the taboo deeper in the game.
The mechanics of condoms would be like, putting it on yourself or asking a character to pose in a sexier way, and when using the condom, ideas are placed on top of the character or in any random place.
It would be cool if a progress bar was added, like lust, if it was too high the character would go after the MC wanting sex.