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I don't think it happened all at once in a single episode. It was more gradual throughout the series. But we do see Inuyasha showing feelings for Kagome as early as episode 6 and 7, even Sesshomaru mentioning he's grown feelings for her. But of course, their relationship is severely hindered by the return of Kikyo, so Inuyasha is not able to fully commit to his feelings for Kagome until Kikyo's death much later on. That's the point when Inuyasha falls completely in love with Kagome.