What does it mean when you dream about your sister's boyfriend is trying to kill you?

In dreams, "death" represents a change or transition from one stage to the next, or the end of something and the beginning of something else. It is also important to know that the dream is about the dreamer, and the dreamer's perceptions. So this particular dream suggests that the dreamer feels that the sister's relationship with that boyfriend is finished. Alternatively, the "sister" could represent the dreamer's self, and the "boyfriend" could be a symbol for some relationship of the dreamer's that is fading away.