I think this whole argument hinges on the definition of "cuck", to my knowledge the person has to get off to it or be in some way humiliated. This is what I base my argument on, and I think a lot of people will agree that an open relationship for example isn't always cuckoldry.
Now having established that, in order for Freddy to do anything at all, Billy has to choose to distract him by offering him one of the two women. If Billy doesn't offer them to him, Freddy doesn't fuck them. Furthermore Billy shows an extreme lack of empathy or affection, so I don't think he cares at all.
Analogy: It's a very different story if some dude steals my beer and drinks it in front of me in my living room or if I give him one of my many beers and we drink a beer each in my living room.
And as far as I can recall it's a gradual increase from kissing to making out to then BJ and sex. Putting the mind control on Steph stopped her from going further than making out with Freddy, so there is a choice, even if not in dialogue form. So maybe it's hindsight, but it's also clearly hinted at that things will escalate if you don't use mind control.
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But I agree that more dialogue options to stop the sharing (or cucking if you think that's what it is) would have been nice. I guess the dev just assumed you were into that because why would you choose that option otherwise. I was also okay with dressing Freddy up and maybe her kissing him, but making out was a bit too far for my taste and I would have liked for there to be an option to step in and break it up.
Same thing with Derek, you can tell Sandra you will think of something else, but at that point the game didn't let me talk to the principal about letting him join the football team anymore, forcing the player to pick a sharing option.