break up has 33 distinct synonyms spread across 18 of its 19 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.
discontinue an association or relation; go different ways
“The business partners broke over a tax question”
cause to go into a solution
“The recipe says that we should dissolve a cup of sugar in two cups of water”
take apart into its constituent pieces
separate (substances) into constituent elements or parts
Synonyms, antonyms and the broader and narrower relations for break up come from Princeton University’s WordNet. Full sources and licences.