Et tu, Brute' ?

Students in English II just read the assassination scene in Shakespeare's Julius Caesar. I can't imagine how difficult it must have been for Caesar to recognize his best friend among the assassins, and I can't imagine how difficult it must have been for Brutus to decide between his loyalty to his best friend and his loyalty to his country.  The other assassins, I believe, acted out of jealousy, not out of a sense of higher purpose.