This guy was insatiable and mistress Alessa was tired of having sex with him. It was becoming boring now as he wanted it all the time. So she had to make sure that she dominated the guy and that she degraded him like he needed to be degraded. She used her fisting to make him learn that he had to tame his urges. The pain he felt as she double fisted him made him change and contain his urges.
Mistress Gaia did not like the bad behaviors that this guy had and for that, he had to be taught a lesson and he had to be punished. That is why the mistress felt that the best thing to do to him was to invite her friend and get her to help her in fisting the guy. He was shocked at what they did to him but he was powerless to do anything about it.