HOPELESS LOVE?

A problem that seems to get very little attention among clinicians, but which we have all seen, is that of the client whose relationship has ended but they can't get over it and move on.  Maybe the relationship used to be good.  Maybe it wasn't.  Maybe the person got "hooked" on the other based on minimal flirtation or other encouragement.  Whatever the particulars, now they are stuck, and often they are really  suffering.  They can't get over this person.  They have reserved a place in their world for this person as their "one and only," and can't make that place available to anyone else. 

Anyone have any status dynamic (or other) ideas that you  have found generally helpful in such (for me, very difficult) cases?