What Does it Mean to be a True Friend?

In Julius Caesar, Brutus is Caesar's best friend, or at least that's what Caesar thought. In Act three Brutus and a bunch of other men stabbed Caesar to death, but the only stab wound that hurt the most was the one made by Brutus. Brutus' stab wound hurt the most because they were best friends. I don't think Brutus was really a true friend because why would you kill your best friend just so you can be crowned instead. If Brutus were a true friend to Caesar he would be happy for Caesar and celebrate with him instead of being jealous. A true friend means you support your friends whether you like it or not.