Lady Stefanie wanted to get this guy to be her paypig so she charmed her way to his heart with her hot body. She enticed him and used her flirting and naughty skills to get him to fall for her. Once he did, she made sure she had total control over him and then she dominated him financially. It was a lot of fun for her and she made money too.
Lady Stefanie loves to make money from married men because she knows nothing can happen between them since they already have families. She cannot have a serious long term thing with a married man and that is why she loves to tease and mess with them to make money off of them and find a convenient excuse to stop it all after she has had what she wanted from them.
Lady Stefanie was angry when she noticed that her boyfriend had been doing crazy things behind her back. She did not want him to learn to do away with her and to find solace in another woman's arms. Lady Stefanie chose to punish him in a way that she knew he would be hurt most, financially. The mistress made him pay for every mistake he had made before she left him alone.