Melancholy (n.) is a fixation not on some lost object, but rather on some object which he possesses but has lost his desire for (because the cause of desire has withdrawn).
Definition.com
Definition.com
Melancholy (n.) is always proleptic. One grieves for the loss that one anticipates.
Definition.com
Melancholy (n.) is about possession. In it's logic, the only way to possess an object that we never had is to treat an object that we still fully possess as if the object is already lost.
Definition.com
Melancholy (n.) is the presence of the object itself deprived of the desire for itself.
Definition.com
Melancholy (n.) is not mourning a lost object but possessing the object and having lost the desire for it — it occurs when we finally get what we wanted and are disappointed.