Whittier

O friend! O best of friends! Thy absence more
Than the impending night darkens the landscape o'er!

Longfellow

What shall I do, my friend,
When you are gone forever?
My heart its eager need will send
Through the years to find you never,
And how will it be with you,
In the weary world I wonder,
Will you love me with a love as true,
When our paths be far asunder?

Mary Clemmer

A man dies as he looses his friends.

Bacon

We call that person who has lost his father, an orphan; and a widower, that man who has lost his wife.... And that man who has known the immense unhappiness of losing his friend, by what name do we call him?... Here every human language holds its peace in impotence.