This guy was misbehaving. Mistress Marlena tried her best to make him change but he did not. She could not let him continue misbehaving and so she had to do what she does best which was to shit on him. The degradation he felt as she did her thing on him was crazy and he never messed up again after what she did to him. He stopped misbehaving after that.
Mistress Marlena wanted to make sure that her boyfriend learned his lesson and that he stopped being insensitive. She had to make sure that she humiliated him and that she made him realize that if he did not stop being insensitive, she would not stop doing random crazy things like shitting on him and making him drink her pee. So it was up to him to decide what he wanted.