In Act 4, Scene 2, Brutus tells Cassius that Portia is dead. Then a short while later Messala enters to report news he has received in letters. He is reluctant to report one piece of news from Rome but finally tells Brutus about his wife's suicide:
Then like a Roman bear the truth I tell;
For certain she is dead, and by strange manner.
Brutus' response seems rehearsed, since he already knows about his wife's death. He says:
Why, farewell, Portia. We must die, Messala.
With meditating that she must die once,
I have the patience to endure it now.
Messala is impressed. He says:
Even so great men great losses should endure.
Brutus is a philosopher, a Stoic. It would seem that he is trying to impress Messala with his strength of character, although he has just told Cassius,
I am sick of many griefs.
Brutus is an admirable character, but there are many places in the play where he shows himself to be narcissistic, overly concerned about his reputation, his family honor, and the impression he makes on others. The reader gets the impression that Brutus wants Messala to spread the word that Brutus is such a great man that he received the news of Portia's suicide with profound wisdom and courage. Evidently Brutus does not mind the fact that Cassius knows he is only putting on a show, his purpose being to have his soldiers believe that he is just such a great man as Messala takes him to be.
Shakespeare apparently believed that all men have their faults--or at least he must have felt that stage characters are only believable if they are mixtures of human qualities, not unlike the members of the audience. His Antony is cunning and dishonest. His Cassius is money-hungry. His Julius Caesar is practically a megalomaniac. And his Brutus is noble but infatuated with his own integrity.