My theory is just a theory. Since SC Stories indicated that the scene in Christian's backyard is foundational to the story, I was trying to think of a potential scenario where Vivian having sex with Christian so quickly made more sense. Christian did make it clear that Hutch told him he was married, but Christian said he thought Hutch was making it up.
View attachment 4657287
View attachment 4657288
One reason why I came up with this is because I think SC Stories could be planning on surprising us by flipping things on their head. I am in no way saying this definitely what is going on, but sometimes good writers trick the audience by leading them down one path only to flip things on them later. That Christian says he thought maybe Hutch was making it up, does cast doubt on Christian not going after Hutch because he thought Hutch was stealing to benefit his family. Christian does however say, "I thought MAYBE he was making it up." This means he did think it was a possibility. Since SC Stories hinted that the conversation in the backyard leading up to Vivian first fucking Christian is so important, I don't see a how something other than a revelation like this would be giving us more than what we know about why Vivian fucked Christian.