If you dream of your boo but wake up sad, it means your intuition (gut feeling) has sent you a message about your romance. You may have picked up subtle indications of how this relationship is going. Despite your attraction for your boo, this relationship does not seem promising.
You should look into yourself and your waking reality, to understand this dream. What are the factors surrounding this dream? Is this dream the consequence of nostalgia for that person? Or is this dream one of desire, because you didn’t get the heart in the first place?