Already finished it.

He leaned down to her offered neck and with open lips he began sucking her below her ear. Sis cradled his head with her left hand and moaned as her flesh swelled into his mouth. She lifted her legs one at a time as he lifted her by her thighs. She was shivering as her neck bruised and her carotid bulged. She could feel his teeth gently gnawing. She was caught by surprise as his cock slid up her pussy. He slowly eased her on, not to cum too soon. She reached around him pulling tight and spoke into his ear, "It's time my love. Take me, drink me in. My life is yours to devour.."
With a sickening "crackle" his teeth ripped open her neck. Sis let out a panicked yell for just a moment and then held tight and started humping her lover's cock. Her arousal was greater than she had ever known and though the pain of his bite made her gasp for breath, his suckling of her blood made her giddy as if each gulp made her orgasm.
Her blood burned in his belly. With each swallow his dick hardened. He began thrusting with her humping, never releasing her neck. His nuts burned to release, he slammed into her violently. She was wailing in pain with each drive of his hips. He was intent on drinking her dry and he did not notice when her pelvis broke. She was crying silently now, too weak to scream. Her blood loss was almost complete. Her arms flailed as he bounced her.
He was blinded by her voice in his head, "More, MORE, MOOORE."
Try as he might, he could not climax. His penis was enormous inside her and he was ready to burst, but he could not ejaculate. He tried to drink more but she was empty of blood and he heard cracking as he continued to rut her. He looked to her face and dead eyes looked back....