I think this is the anal scene with Christian
We can deduce that Christian was the first guy to deep throat Vivian from the conversation between them in the kitchen, and a bit with the "one small step..." comment in the bathroom. The bitch didn't even put up any real resistance, probably enjoyed it all, as we can tell from the bathroom scene.
Having her lose her anal virginity to Christian too, would be too much. Plus I know these games use porno logic, but the writing is pretty good sof ar, and going by that, there is no way she is going to be able to stuff a fat dick like that up her butt without a hell of a lot of prep work, tons of lube and a long time of gradual sphincter stretching to get there. Come on let hutch have a win too, after all she did offer him first dibs, and deny Christian in the bathroom.
We also see a submissive side to Vivian when she's with Christian, here for example.
Yeah that was painful, it's probably what broke Hutch. Especially the scene where they are looking into each others eyes passionately, romantically even, while he is banging her. Looks like there was some love and connection there and not just lust.
For me the game is about how far will Vivian go from loving wife to the bosses fuck toy and how much is Hutch willing to put up with to save his marriage.
She is not thinking with her heart, or her brain, but purely with her cunt at the moment, so I'd say she has already gone quite far.
Hutch will probably hit rock bottom before hopefully dragging himself up. That is unless this story follow the typical NTR tropes (fingers crossed it steers far away from them, and stays original).