You know someone matters to you if they can betray you, or be betrayed by you. Once there is a possibility of betrayal a great deal has already happened: there can only be betrayal if there is a history, a real relationship or affinity. Betrayal is only possible when there is something to betray; that something takes time, and is of paramount importance. Sexual jealousy is not just one of the things that happens when you become attached to someone: it is the sign of attachment.