I've downloaded a lot of dialogues from multiple sources, but a search for 'vampire' only returned one result. But hey, you're sort of lucky, since it's about a slutty willing vampire girlfriend, and it even has some nice story and interaction (dialogue is over 100kb).
I can't credit the original author though, this dialogue is from an archive, and I have no idea who the writer is.
Description:
It's long been said that vampires must feed on the blood of the living, but this appears to just be myth. You've just discovered your new girlfriend is a vampire and she informs you about the truth of vampires: they feed on the blood and/or the cum of the living. Since it'll help keep her alive, you agree to give her all she needs.