Within all of us human beings resides hurt and pain. These feelings buried deep within us are the results of deeds done to us in past lives as well as this life going all the way back to our births. These events cause emotional memories to actually be hidden in our psyches as well as our physical bodies. Eckhart Tolle in his wonderful book "The Power of Now" does a superb job of explaining this experience and even has a name for it calling it the "pain body".
When a new love comes into our lives at first we only experience the bliss and merging of the wonderful "feeling" called love. Everything is beautiful and we cannot conceive of a time when this sublime feeling will subside. But subside it will eventually, whether it be for a minute, a day or a lifetime. The amount of time we are unable to access love is really up to us.
Sooner or later our lover will do or say something that will trigger our pain body and take us back to the hurt and pain we experienced before. We may not even be able to consciously remember the exact event where this hurt originated but our souls and our bodies will remember for sure and we will expereience this pain all over again as though this love was the original source of it. We all experience it differently whether it be a tightening feeling in our throats or solar plexus or just a feeling of fear that makes us want to run away.
The reason many lovers are brought together is to activate this pain body in each other so that it can be brought into conscious awareness and be healed. It is no accident that we are attracted to who we are attracted to. In his book, Eckhart Tolle gives us some wonderful advice as how to deal with this experience. When our love or anyone else "hits a nerve" with us and activates our pain body it is our clue to not strike back as difficult as that might be, but instead to stop and look inside and see what is really going on. If we can just take a moment to still our minds and actually just feel the feeling that we are experiencing and not run from it, but just stay with it, much in our lives can be transformed and healed.