Obsession: You Belong to Me
Forward and Buck believe that rejection is the trigger of obsessive love. They state four conditions to help identify it, namely, a painful and all-consuming preoccupation with a real or wished-for lover, an insatiable longing either to possess or be possessed by the target of their obsession, rejection by or physical and/or emotional unavailability of their target, and being driven to behave in self-defeating ways by this rejection or unavailability.
Obsessive lovers believe that only the person they fixate on can make them feel happy and fulfilled.
Persons close to the love-obsessed can also be greatly affected. Witnessing a friend or family member suffer from the disorder can be distressing.
From http://en.wikipedia.org/wiki/Obsessive_love