saudade

As defined by Wikipedia: Saudade has been described as a "vague and constant desire for something that does not and probably cannot exist ... a turning towards the past or towards the future." A stronger form of saudade may be felt towards people and things whose whereabouts are unknown, such as a lost lover, or a family member who has gone missing. It may also be translated as a deep longing or yearning for something which does not exist or is unattainable.