fixated
To be fixated on something is to be focused on it to the point where you can't think about anything else. You might be fixated on a problem that you're trying to solve, or you might be fixated on a person or object that you find attractive.
She was fixated on the idea of moving to a new city, and she spent hours thinking about it.
He was fixated on the wrong target, and he was killed because of it.