Martin (1977), directed by George A. Romero, follows a young man who believes he may be a vampire. Living with relatives in a declining industrial town, he struggles with his identity while committing acts of violence. The film presents an ambiguous portrayal of vampirism, blending psychological elements with grounded realism.

A troubled young man, who believes himself to be a vampire, goes to live with his elderly and religious cousin in a small Pennsylvania town where he tries to redeem his blood-craving urges after he falls for a lonely housewife, all the while his hostile cousin becomes convinced that the young man is actually Nosferatu.

Från IMDB:
A young man, who believes himself to be a vampire, goes to live with his elderly and hostile cousin in a small Pennsylvanian town, where he tries to suppress his blood-lust.