I can see how this obsessive thinking works!  I think for me I become obsessed because I am constantly looking to fill the void I feel with something from another person.  I become convinced that, when I feel that lacking, it can only be filled by X person.  Then I feel something amazing from X person and become convinced that I cannot breathe and cannot survive without that person because when they are removed from me that lacking then becomes this gaping hole because I had been so fulfilled when I had been with that person. Of course the trouble with that is that it will NEVER be a sufficient basis for a relationship.  The person (like April says) will eventually get suffocated by that neediness and you (or I) will never feel fulfilled because even if that person doesn't actually "leave" the relationship, they'll always not be giving enough, or not have enough space to come to you, or what have you.  I just know that for me, as much as I miss my AP (desperately at times) the structure of our relationship as it was was not workable.  I was too needy and too unhappy with myself. Oh, and BB, unfortunately yes, therapy is LOOONNNGGGGG and there is no one session, book, or pill to make it all better or to find the answer (I am reminded by my therapist of that almost every session!).  Keep at it and you'll be surprised at what you uncover about yourself.