obsess

to take up so much of someone's thoughts that they cannot focus on anything else, often to an unhealthy or unreasonable degree — for example, when a teenager keeps replaying a single argument with a friend, or a writer cannot stop checking sales numbers for her new book.

• preoccupy

  more neutral; can describe ordinary worries, not just unhealthy fixation.

• consume

  stronger and often used of emotions like jealousy or grief that take over a life.

• fixate on

  phrasal verb; suggests narrowing attention onto one detail, often unreasonably.

• ignore

  the opposite action: paying no attention rather than too much.

• dismiss

  to push something out of mind quickly, the reverse of dwelling on it.