Complex sentence: Kotaroh's family were labeled as demons by the villager and since Misha was Kotaroh's emotional support, he committed suicide upon discovering Misha was prohibited by Heaven from returning to the human world.
Split into simpler sentences: Kotaroh's family were labeled as demons by the villager. Since Misha was Kotaroh's emotional support, he killed himself upon discovering Misha was prohibited by Heaven from returning to the human world.