The Villainess' Wise Retirement Plan

I've transmigrated into a game I used to enjoy playing, "The Demon King's Consort," as the villainess who dies after harassing the female lead! Worse still I have a terminal condition! As a human mana stone, the more I use magic, the more it drains my life force... What kind of life is this...? No matter. I can simply just choose not to use magic, right? I'll preserve and protect my mana (= life force), gather a slush fund, and run away with my big sister to a warm and peaceful southern country...! Or so I thought... "Take it, Lillian. It's your doll." My Father threw the male lead at my feet. The obsessive male lead that was destined to become a psychotic, possessive king in the future...!