【Addict】 , 【votary】 , 【devotee】 and 【habitué】 designate a person who by habit and strong inclination indulges in something or the pursuit of something.

【Addict】 implies excessive, continuous, and often compulsive indulgence typically in harmful but sometimes in harmless things.

• a drug 【addict】
• a detective-story 【addict】

【Votary】 and 【devotee】 retain some of the implications of their religious senses such as enthusiasm, often amounting to fanaticism, and zeal. They rarely suggest attachment to that which is degrading or debasing but they do not invariably imply attachment to that which is uplifting.

• a 【votary】 of science
• a 【devotee】 of vegetarianism
• any worthy object of study, pursued disinterestedly . . . does not permit its 【votary】 to be very seriously narrowed by his zeal
  —Inge

【Habitué】 implies frequent attendance at a place but it commonly also connotes habitual indulgence in a pleasure.

• a 【habitué】 of the theater is a 【devotee】 of the drama
• a 【habitué】 of a gambling house is a gambling 【addict】