Cheap. SPOILER. Cheap because the series develops and brings viewer to believe certain truths, to believe what we are seeing over several episodes only to declare it all a lie in the end.
I find it a cheap cinematic trick when directors do this.
Granted it's easy to understand why Catherine lied or hid the truth. But I am referring to the director lying to the audience. It's deliberate. The series leads you to believe it was an affair. So many scenes, so many details, such time spent on developing that relationship. And especially because so much of the series is narrated by the characters including Catherine who says in narration, "Robert wonders if you blame Nicholas for your lover's death". Would Catherine think in those words after the truth is revealed?
I dont like projects that rely on flipping the viewer's reality. I think it would have been much more fair, if in the several parts that turn out to be untrue, they introduced those scenes via the novel, say Robert reading various parts of the book. Then as a viewer I have been introduced to those events through Mr/Mrs Brigstock's (the novel's authors) perspective. In that way I wouldn't feel lied to.