Diddy believes Cassie Ventura, cheated on him with professional bull rider/ personal trainer Alex Fine, a source tells PEOPLE. Diddy feels betrayed after learning that Cassie supposedly cheated on him with the trainer he paid for. Diddy hired Fine, 25, as Cassie's personal trainer after Diddy's trainer, Jamal Liggin, got so busy that he had to hire backup. Diddy and Cassie broke up around October, after being together more than a decade. By late December, Cassie and Fine were sharing photos of the two together on social media, including a photo of Fine, Cassie and her mother in a photo booth at a holiday party, according to Us Weekly.