1) Be preoccupied 2) Be preoccupied with 3) Be preoccupied with something 4) Be too single-minded 5) Be totally preoccupied 6) Be unable to let something go 7) Be very single-minded 8) Become completely absorbed 9) Become fixated 10) Behave monomaniacally 11) Beset 12) Constantly worry 13) Consume 14) Control Found on https://www.crosswordclues.com/clue/obsess
Ob·sess' transitive verb [ Latin obsessus , past participle of obsidere to besiege; ob (see Ob- ) + sedere to sit.] To besiege; to beset. Sir T. Elyot. Found on http://www.encyclo.co.uk/webster/O/5
obsess, obsesses, obsessing 1. To dominate or preoccupy the thoughts, feelings, or desires of (a person); beset, trouble, or haunt persistently or abnormally: 'Suspicion obsessed him.' 2. To think about something unceasingly or persistently. 3. To occupy someone's thoughts constantly, compulsively, and exclusively: 'The desire for vengeance obsess... Found on http://www.wordinfo.info/words/index/info/view_unit/3417/