fixate has 2 distinct synonyms spread across 2 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
attach (oneself) to a person or thing in a neurotic way
“He fixates on his mother, even at the age of 40”
pay attention to exclusively and obsessively
“The media are fixating on Princess Diana's death”
Synonyms, antonyms and the broader and narrower relations for fixate come from Princeton University’s WordNet. Full sources and licences.
make fixed, stable or stationary
“let's fix the picture to the frame”