Revenge is a Dish Best Served Lusty

Asmodeus!AU, Cult!AU. Parvati has just broken up with her girlfriend Lavender. She just wants to go out and have a rebound sort of fling to get over Lavender. But what happens when Lavender's plan for revenge is exactly hinged on that? What will happen when she hooks up the possessed Romilda Vane? Will she fall in love and most of all will love be able to break the demon's hold?