While I haven't played the last 2 updates, in this game (and the developer's other game) it is the MC (you) who need to encourage the girls into sharing/swinging. It's not like you have to “protect” them from fucking someone else because they want to. It's that you as the player choose options that entice them to fuck other people.
At least with the girls in the family (mom and sister). I don't remember if it's the same with the rest of them.
And better yet, you can totally disable that content and you won't even see related options in your game.
Although I don't know what percentage of the game will be focused on non-sharing, considering that, according to the changelog, it looks like there are basically four routes: Virtue/Vice and Sharing Virtue/Sharing Vice.
MakinWaves Could you clarify this for me? Please. Sorry to tag you.
Hope that helps, Benny.