obsession

noun
  1. A persistent, disturbing preoccupation with an often unreasonable idea or feeling. noun
    His obsession with cleanliness made it difficult for him to relax.
    She has an obsession with collecting vintage dolls.
  2. A state in which someone thinks about someone or something constantly or frequently, especially in a way that is not normal. noun
    Her obsession with social media began to affect her daily life.
    The artist's obsession with light and shadow is evident in his paintings.