Mistress Xenia knew her boyfriend was wasteful and since he was not the type to invest his money, she chose to do it for him. And she did this by making him pay for things that he would routinely not pay for. Like how she would pretend that they were doing foreplay and she makes him pay for it and for some of the other naughty things she did to him. And slowly, she accumulated the money and she invested it for them.