That's not sexual content, unless these scenes are implemented in the game.
I can't imagine a plausible scenario in which they currently fuck, either. But that isn't what was asked about. Its about future potential scenes and in that regard, only your imagination is the limit. The no brainer is simply be Cooper and Carmille be swingers, which is entirely consistent with their carefree personalities. Cooper could be cool to lend her or its a fair foursome.
The demand to hog her for yourself and cuck Cooper is at odds with the current friendship the MC upholds to him. If over the course of the game, Cooper can become more and more an annoyance, if not an (unwillingly) detriment to MC (the money he gifts him with could backfire horrendously), a MC who may develop further on the ruthless side, could end up antagonising him fairly plausible. Carmille would need to be develop further as well to justify why she would be on bad terms with Cooper, but since we know significantly less about her, there is much more room to move around. The two scenes with her and MC already set up a playful relationship, so expanding that already existing bond is doable, as well.
Going from the current development log and which character it adresses, its clear that Carmille is not on any high priority to expect anything soon. But the same can be said about Patricia and some other women who were barely introduced.
Wendy is already established and bar some expansions finished. This game is still in development, we don't know entirely in which direction it expands. So your comparison doesn't hold up.