Preoccupy, fixate (6)
I believe the answer is:
obsess
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">preoccupy</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(obsessing is a kind of preoccupying)</span><br/ ><br/ >'<span class="explanation-format__original">fixate</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for obsess that I've seen before include "Prey on" , "Control" , "Persistently preoccupy" , "Be constantly talking about" , "Preoccupy continually" .)