Last Night I Had A Dream.i Saw My Cousin Killed And A Lot Of Blood.what Does It Mean?

Dream analysis is barely even a pseudoscience, with very little empirical support.  Dreams tend to be random images and associations thrown up from the memory as the brain organizes itself while you sleep.  The most I would feel comfortable saying for certain about your dream is that it contains a merging of two themes:  Loss of a family member, and violent death.  Violent murder with a lot of blood is something of an archetypal fear; that is, most people are afraid of experiencing it or seeing it happen to someone else.  Losing a family member is the same thing; almost no-one wants to see a member of their family killed.  I would say your dream is a visual manifestation of two fears, and while it was disturbing, it doesn't have any reliable ties to future events.  I know there have been cases where dreams have preceded events, but they are few and far between, and a lot of them are just mathematical coincidences.