To dream about a crush means that the dreamer is thinking about this particular person on both a conscious and unconscious level. If the individual in the dream appears distant, this often points to a fear of rejection that the dreamer experiences in waking life. If the individual in the dream is open and loving, this represents what the dreamer wishes for in waking life.
Dream symbols take on a wide variety of meanings, but in the case where one dreams about the object of their affection, the most basic reason is that they hope for a deeper relationship with the person in their dreams.
Dreaming about loved ones is quite common. In addition to dreaming about current crushes and love interests, many people experience dreams about loves from the past. When a past love shows up in a dream, it often signifies unfinished business. Dreaming about a past love also signifies that the dreamer is not ready to let go of their past. Documenting dreams upon waking with a journal or electronic voice recorder is a helpful way to analyze dream themes, especially recurring dreams, because the human brain tends to forget about the specifics of dreams very quickly.