Obcession

ob·ses·sion

əbˈseSHən/

noun

noun: obsession

1. 1.

   the state of being obsessed with someone or something.

   "she cared for him with a devotion bordering on obsession"

   • an idea or thought that continually preoccupies or intrudes on a person's mind.

     plural noun: obsessions

     "he was in the grip of an obsession he was powerless to resist"

     synonyms:

     fixation, ruling/consuming passion, passion, mania, idée fixe, compulsion, preoccupation, infatuation, addiction, fetish, craze, hobbyhorse; More phobia, complex, neurosis; informala bee in one's bonnet, hang-up, thing "that new car has become his obsession"

Origin

early 16th cent. (in the sense ‘siege’): from Latin obsessio(n-), from the verb obsidere


That pretty much describes it -