What is the end of a close relationship? (Part I)

Being connected with others is  obviously a basic human need. So we are looking for trustworhty people to share our feelings, thoughts, interestings, etc.
Sometimes we are lucky to have a close relationship with our male and female friends. However, who can honestly say they felt happy or at least comfortable when their close relationship ended?
Of course, we want our happiness to last forever. But as they say, "along with death and texes, the only certainty in life is change."
And our relationships also change all the time. Early or later, we can find the conversations with our best friend rather boring. Or we can no longer trust him/her. Or we can face unequal power or other negative things in our relationships.
Whatever the reason, a sense of disappointment seems to be quite unavoidable.