Tell me what company you keep, and I'll tell you what you are.
Miguel de Cervantes
A friend is, one might say, a secondself.
Cicero
Trusting no man as his friend, he could not recognize his enemy when the latter actually appeared.
Nathaniel Hawthorne
It is a great confidence in a friend to tell him your faults; greater to tell him his.
Benjamin Franklin
Friendship is a disinterested commerce between equals.
Oliver Goldsmith