For example, it'd be great to have Sarah and Alex invite over Alex's intern for dinner, and they end up having a threesome or Alex bangs her while Sarah enjoys watching or they invite over one of Sarah's potential paramours for either threesome or Alex watching.

just a thought... Alex watches Sarah and the intern...

and maybe, that interaction involves a strap-on, maybe Sarah using on the intern... while Alex watches.
Then Sarah has Alex join in, by making the intern suck his dick while Sarah's doing her thing...
Or Sarah and the intern switch places...idk, just brainstorming here...
What I "dislike" about some of the route/stat build ups in most VNs/games, is when they cause a loss of choice control.
For instance, Sarah doing her things with Neil and the other dude, it's building lust/desire or whatever, and that's not necessarily a bad thing, it's a good game/tease for the couple. It can open opportunities to explore, without locking them into a collision course with total destruction.
So many VNs get so close to getting this just right, then poof...it's gone.
It'd be nice to build that, go right up to the edge, but then have the chance to go nope, and step back...
I mean, I get if there's a cheating/NTR route, it's expected. But the NTS/swinging/hotwife routes, many just don't quite seem to get "it"...
I wouldn't mind Alex and Sarah actually "using" Neil in their own personal couple's fantasy game.
Just let Alex & Sarah remain in control of their choices/actions rather than being a slave to stats or Neil's designs...
It would be awesome to have Neil think his plan is working, only to find out he's the one being used for the couple's own enjoyment... Something along those lines anyway.
Regrettably, it's almost inevitable that we all each start developing our own story progression ideas, expectations, how we'd like to see things play out. And that's usually where so many get disappointed and disgruntled. Unfortunately, cannot please everyone...
I may not like something, but I'm generally ok, supportive of devs doing their thing, even when it's not what I want or expect.
Kind of like The Half Blood Prince movie...

Was the first of that series where I read the book first, and had expectations of how I thought the movie should go... And then the actual movie fumbled it horribly... Walked out of the theatre going that's the worst movie I've ever seen...

Had to watch that thing 3 times before I finally realized, ok, in movie context, it works, and was actually pretty damn good.
From that point on, have finally learned to just appreciate entertainment creations for what they are, not how I want/expect them to be. Except Star Wars...

George totally botched the prequels, kept trying to ruin the originals, and well, it's just been a disaster after that... So for me, Star Wars is and will always be the original theatrical IV, V, VI and the EU with Jaina Solo...
Anyway, you've got a very good thing started with
Whispers of Desire [v0.15] [Mr_Fable].
Looking forward to seeing what you have in store for us going forward.