I agree with most is said above, just one more thing : to me the body language and tone of the conversation while Cleo and Axel were preparing the bed, seem to show that Clara warned Stas about how those games can end and was slightly apprehensive. I think that she was worried that going too far at least so soon might endanger their relationship. He left quite assured, leaving Clara behind for a short moment tempted and wondering...
When they were all naked and they had to decide whether to stop or go on,Clara here seems to ask "are you sure ?"
Stas, sometimes looking at the camera, took decisions as where to place themselves, etc. He clearly was the leader, I think, Cleo & Axel eagerly following.
A few more pictures of what followed.
When Stas decided to go (after all, he has to go to work...) Clara pronounced at one moment the word "massage" which seemed to get everybody's agreement. Maybe we will soon see her introducing Cleo to her Mr Black sessions ?