Interestingly, there seems to be the proverbial game of cat-and-mouse in Scene 3 of Act IV when Titinius and Messala enter the tent of Brutus, who tells Messala that he has received news that Octavius and Marc Antony are bearing down upon them with a mighty army. Messala concurs, and he adds that Antony has put to death a hundred senators. Messala then interjects a quiet question, "Had you your letters from you wife, my lord?" Brutus tells him that he has not received anything even though he really has, and he demands to know what news Messala bears. Then, Messala gives Brutus the news that Portia has eaten burning coals and killed herself. Stoically, Brutus replies,
Why, farewell, Portia. We must die, Messala.
With meditating that she must die once
I have the patience to endure it now.(4.3.212-215)
Unbeknownst to Messala, Brutus has already told Cassius that Portia is dead. And, when Cassius exclaims, Brutus stoically tells him,
Speak no more of her. Give me a bowl of wine.
In this I bury all unkindness, Cassius. (4.3.177-178)
Knowing that others watch him and that Messala is aware of the dissension between himself and Cassius, Brutus may feel that he needs to steel himself against displaying emotion. Instead, he encourages Cassius to act, telling him,
There is a tide in the affairs of men
Which taken at the flood leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures.(4.3.244-250)
This fatalistic observation by Brutus is also somewhat out of character for him, as well, further indicating that he is focused upon the forthcoming battle.