I soooooooooooooooo know what you mean! I am the same way! Actually I had started to believe that I was the only person like this. This is really not a good way of being as I've discovered. I have also discovered that there is no way of changing it either, because it has to do with ones character. Here is the effect that this has had on me:
Fell madly in love with this one guy at age 18. We were together for 2 years. We matched brilliantly and the future was beautiful up ahead. One day he woke up and just decided that he didn't love me anymore. Just like that. My world was crushed. I lingered into the mess of "what happened?" for 5 full years. I ruined and crushed two other people during those 5 years who attempted to be with me because of the hurt I kept holding on to.
At the age of 26 this new person walked into my life. I felt for him things that I thought I would never feel again. I was happy again but still, even then, shadows of the past kept creeping in. With time I decided to let go and freely dive into this relationship. Once again the future was brilliant. In exactly the same way, three years later, and after being the perfect couple...he wakes up and tells me that he doesn't feel love for me anymore. Just like that. I am currently swimming in an ocean of "but what happen? what did I do wrong? how can I take things back how they used to be? why me?"
And my future now??? It will take me a good 5-6 years (just as before) to clean myself up from the memories. The worst pain is that he has moved on ALREADY and is in a new relationship. I am alone and the idea of being with somebody makes me cringe due to my hurt. I am unable to move on. Seriously! I cannot do it. And I do panic because I am 30. In 5-6 years I'll be 35. Who will care to be with me then? So there you go....unable to let go = alone.