What are the two reasons that Brutus gives for Portia's suicide?

Brutus has two different reactions to his wife's suicide, and I believe that like anyone else he kept himself private for the masses and opened up to his friends.

With Cassius, he answers his friend, and he shares his distress. Portia didn't want Caesar dead; she's a friend to Calpurnia and feels like she's an accessory because she's overheard Brutus and the other men planning. With the rest of the men, Brutus seems uncaring about her suicide.

Actually, Brutus tells us the reasons:   

      BRUTUS   

                               Impatient of my absence,   

      And grief that young Octavius with Mark Antony   

      Have made themselves so strong—for with her death   

      That tidings came. With this she fell distract,   

      And, her attendants absent, swallow'd fire.  

Portia was distraught because Brutus had been gone so long and because she feared that Brutus would be defeated by his enemies. Brutus fled Rome for his life after Antony's momentum-changing speech, the turning point of the play and has been trying to raise an army in Sardis, Asia Minor, so that he can fight Caesar's avengers and take back Rome. Portia and Calpurnia never enter the same scene or speak of one another, so I find the first answer quite interesting since there is no textual evidence of their relationship. Perhaps a Plutarch scholar could tell us more...

When speaking of suicide and Caesar one cannot help but point out that immediately after receiving the infamous Ides of March warning, he dismissed his personal guard, as well as his surreptitiously altering his will just days before to transfer a huge sum to the Dole (welfare).

Julius Caesar basically committed suicide, not entirely unlike what we call today, "death by cops". Except that he was not defeated in death, quite the opposite, the liberals, such as they were, utterly defeated the conservative Optimates that opposed Caesar. His victory was total and complete.

(Note: he was suffering from temporal lobe epilepsy, so his sacrifice was not so appalling, but rather a strategic use of his state of health.)