Inter-fusing, which means the merging of two or more things, can have several antonyms depending on the context. The opposite of inter-fusing could be disintegrating, separating, dividing, splitting, or disconnecting. These antonyms refer to the act of breaking apart, isolating, or disconnecting something that was previously joined or blended. Disaggregating, compartmentalizing, isolating, alienating, differentiating, and disuniting also represent antonyms of inter-fusing. It all depends on what you want to convey with the word choice and the context or setting of the conversation or text. Using the appropriate antonym of inter-fusing can express precisely what you want to communicate.