Preoccupation is a state of mind in which you think about something so much that you do not consider other things to be important. It was hard for him to be aware of her; he kept sinking back into black preoccupation. = obsession
the mental state of being preoccupied by something an idea that preoccupies the mind and holds the attention
{i} being lost in thought, being occupied with meditations; obsession, fixation; thought that is constantly on one's mind; previous appropriation, prior tenure or possession
If you have a preoccupation with something or someone, you keep thinking about them because they are important to you. In his preoccupation with Robyn, Crook had neglected everything