I'm not aware of WWG addressing this directly, and I doubt he will. Sometimes leaving certain things up to the audience to interpret for themselves is much more artistic and powerful. In other words, there's no right or wrong answer. That said, I do have my own opinions...
There are several recurring themes in the story, including the importance of being in the right place at the right time, and people being slaves to their own wants and needs. These concepts are fully understood by Hunter and he tries to use that knowledge to his advantage. He explains as much to Sterling during their conversation on the very first night, and it's hinted at by the very title of the game ("Power Vacuum").
It's a cynical and unromantic perspective, but there's some truth to the idea that people will eventually fall for each other if they have no better options. So the best strategy is to position yourself to be the one to fulfill someone's needs, financially, emotionally, and sexually, until they convince themselves that they love you. But it's not like the women don't love Sterling, and if given the choice they'd obviously pick him over the alternatives, but at the end of the day they're women with needs. If Sterling is not available to fulfill those needs, they will find someone else who can, it's just human nature.
I'm not quite sure how to reconcile the above with the scenarios where the women have already fallen for Sterling, and then they fall for his rivals while he's still around...
In the Kevin ending, I think we can "blame" the first sexual encounter on the wine and the gas, but the second encounter is more difficult to "excuse": Ophelia was in right mind but was overcome with lust after seeing Kevin's buff body and remembering the pleasure of their first encounter. Afterward, I think her intentions were to continue fucking both Kevin and Sterling, and I can't help but wonder how Sterling would've reacted to this.
In the Brenna/Drew/Hunter ending, and the Brenna/dogs ending, my impression is that Brenna would likely keep fucking Sterling while also continuing these other escapades in secret, unless she got to a point where she was no longer satisfied by Sterling.
But I may be reading too deep into things. It's also perfectly likely that the "canon" women would not do the things we see in the alternative endings, and that these endings exist for "shock value" (as mentioned earlier). It's all open to interpretation, and honestly I think I prefer it remain that way, rather than having WWG explain it too much.
