Excellent, but was thinking more of a Cloaker, Soulleecher, or Succubus. These creatures seem safe/helpful or innocent, but then attack, draining your life force and leave you as a discarded husk.
Not really sure what he is but this comes immediately to mind: https://en.wikipedia.org/wiki/Strahd_von_Zarovich
"He is a malignant narcissist trapped by his malignant narcissism – forever alone, forever feared and unable to change. Salvation is beyond him. He is framed as inhumanity personified, often serving as a cautionary tale: once you lose your humanity, you can never get it back."