To see your cousin in your dream represents something or some aspect of your character that is somewhat familiar. Perhaps you need to spend more time in cultivating and developing some emerging ability or character. In particular, if you dream that your cousin is ignoring you, then it indicates that you are not acknowledging some aspect of yourself that is represented by your cousin.
To dream that you or your sibling is in love with a cousin represents your acceptance of each other. You are acknowledging and embracing key qualities in one another.