Unfortunately for your preference, I've nearly never heard of anything like that. Almost all the games fall on either extreme of that preference, either the girl will be committed to mc and he'll direct her what to do and she'll be timid to do it on her own, or the girl will take the initiative to do stuff with others but it'll have heavy ntr overtones and she'll usually deceive or humiliate mc.
Yah great it'd be nice to hear others thoughts and preferences.
My own would be fairly similar to yours, a standard game with a well-developed non-sharing story where mc is in a committed relationship with a girlfriend and they decide to spice things up with sharing liasons.
Almost no game has what I really want which is
the emotional aspect kept light yet the sex kept intense; usually the most explicit (penetration close-ups/rough sex/etc) sharing sex scenes are seen on more ntrish paths, and the pure sharing paths where the girl is still in love with mc are more "softcore" versions. Secret Care Cafe comes close to this, but I can't get into cartoon graphics as much as 3d daz.
For those of you who've played Being a Dik or College Kings, imagine Maya or Nora going along with a threesome event because they love you and are willing to get wild. (and end up enjoying it themselves! - I HATE "sharing" setups where the girl just ends up being abused by some ugly hobo)
imagine something like:
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My ideal sharing game would have the graphics and story of Being a Dik, with the sharing emotional lightness of Secret Care Cafe, with the sex animations of Horton Bay Stories.