ob·sess
əbˈses/
verb
preoccupy or fill the mind of (someone) continually, intrusively, and to a troubling extent.
"he was obsessed with the theme of death"
synonyms: preoccupy, be uppermost in someone's mind, prey on someone's mind, prey on, possess, haunt, consume, plague, torment, hound, bedevil, beset, take control of, control, take over, have a hold on, rule, eat up, have a grip on, grip
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(of a person) be preoccupied with or constantly worrying about something.
"her husband, who is obsessing about the wrong she has done him"