Without love our life is ... a ship without a rudder ...
like a body without a soul.

~Sholem Aleichem

Perhaps a great love is never returned.

~Dag Hammerskjold

The silence that guards the tomb does not reveal God's secret in the obscurity of the coffin, and the rustling of the branches whose roots suck the body's elements do not tell the mysteries of the grave, by the agonized sighs of my heart announce to the living the drama which love, beauty, and death have performed.
-Kahlil Gibran

For all sad words of tongue and pen, the saddest are these, 'It might have been.'
-John Greenleaf Whittier

The end comes when we no longer talk with ourselves. It is the end of genuine thinking and the beginning of the final loneliness. The remarkable thing is that the cessation of the inner dialogue marks also the end of our concern with the world around us. It is as if we noted the world and think about it only when we have to report it to ourselves.
-Eric Hoffer

Oh, sweet sorrow, the time you borrow, will you be here when I wake up tomorrow?
-Katherine Wolf

The absence of love is the most abject pain.
-Herr Lipp

http://www.sad-quotes.com/sad_words/sad_words_011.htm