This mistress does not like people who are too proud. This guy was and he was like the proudest person she had ever encountered and she did not like it. So she had to come up with a way to dominate him and ensure that he would never do it again. She cruelly cuckolded him and he was so shocked at what she did that he had to rethink his pride.
This mistress had an issue with this guy for spreading rumors about her. She did not want her name to be spoiled for no reason and so she had to do something about it. She chose to use her cuckold fetish to dominate him. She knew he wanted her and since she did not have time for him, he resorted to the rumors. And so she had an easy time cuckolding him and humiliating him before warning him of worse if he did not stop spreading the rumors.