My Precious Mate
Harry is dying, Hedwig flees trying to find some help. Eventually Severus realizes Harry is his mate, turns him and trains him and his friends for the war in his manor. They come back stronger than ever to finish it once and for all.
Harry was betrayed by the Order and the Wizarding world after the defeat of Voldemort. They Obliviate him, and leave him thinking he deserves what they did to him. With the help of a vampire, he learns to live his immortal life without fear and hurt.