Why would someone break their friendship? In most cases it is hard to express the actual reason why you are ending a relation. Usually people try to make a distance at first. If the message is not passed, might start making up little white lies that would eventually end the relation making him or her feeling bad.
The truth is once the friendship is infected, or has a slight fracture it cannot be mended. Even if they let go of the past and become friends again they cannot be the same. They cannot share the same degree of intimacy or intensity.
I myself have witnessed such an end to a friendship of two of my very dear friends. And it is really heart breaking for not knowing the reason why it ended. I being a friend of both, have a hard time being with both of them, as one would never prefer to be in the same place as the other. Friendship is one of the greatest gifts that one would get. Try not to lose one. i am also struggling not to lose any.
