My point is I disagree with that premise. How I fill in the missing content leading to the backyard is Christian and Vivian had a conversation about Hutch and his job, at some point he guides her outside they continue to talk, Vivian doesn't like the way the conversation is playing out, and she could've said something like "okay I know what you really want". She lifts her dress up without Christian asking, lowers her panties put her hands on the table, and says you have ten minutes. She probably thought she could get Christian off (which is why she makes note later that she knows how to get him off now) before Hutch would finish writing on his notepad. However once she let him enter her she was overwhelmed by the feeling, and how much she was enjoying it, which led to where we are now and why I'm now leaning towards Vivian being the one who initiated sex the first time. I can see it the other way to, but given the current story, I find it harder to believe he forced her to bend over, and took her by force.
Also my thoughts on this story has no bearing on what I think about real life relationships (outside of even if I chose not to divorce her for financial reasons, no way would we still live together, and if we saw each other in public I'd have no interaction with her), or felonious assaulters so please stop bringing up real life, because I consume this as a fictional story not a window into real life relationships, or violence against women.