Vampire: The Masquerade has an interesting take on the relationship between vampires and their repeat sources of blood.
Basically, a vampire can feed their blood to a human to make them a "ghoul." For all intents and purposes just a human in their prime. Roll back the clock a bit, enhance their strength, that sort of thing. But if a vampire feeds the same ghoul three times, they basically form a sort of link, the ghoul gaining an obsessive level of devotion to their Vampire in a half-drug, half-cult sort of way.
In the game, you can find a woman, Heather Poe, bleeding out in the Hospital level. If you save her by feeding her some blood, she tracks you down. You can either do the right thing and convince her to forget she saw you, or feed her again to make her a live-in source of blood and money.