Grief in a dream usually reflects a loss you're actively processing, whether that's a person, a relationship, or a version of your life that's ended. The dream can be an unusually direct space for that processing to continue, letting you feel and let go of something at a pace your waking mind hasn't allowed yet.
Always deliver judgements from the Stars in general terms, or if thou dost otherwise let it be when thou hast very evident testimonies and in great and weighty matters. - Cardan Girolamo (1501-1576)