Question: why does oroonoko kill imoinda?
Answer: To avenge his honor, Oroonoko vows to kill Byam. He worries, however, that to do so would make Imoinda vulnerable to reprisal after his death. The couple decides that he should kill her, and so Imoinda dies by his hand. Oroonoko hides in the woods to mourn her and grows weaker, becoming unable to complete his revenge.