If he wanted to ruin her life by cheating the boyfriend as a crazy sex slut, why not moving to another body? Unless he likes living that kind of life, but still... the artwork of this gallery, on the other hand, is above average.
@ElisaG He said right in the story: He loves Rumi and was angry she "betrayed him" by being with another man. By becoming her, they are "always together" and she can never "betray" him then bc he would "never betray himself". Warped logic, but he's not exactly sane of course.