Once Brutus has joined the conspirators, can he turn back?
Brutus does not seem to be the kind of man who would turn back after doing so much soul-searching. Conceivably he could turn back, but that would leave him in a dangerous position. He would either have to stand by and do nothing while the other conspirators went ahead with their plan to assassinate Caesar, or else he would have to turn against them and warn his good friend what the conspirators were planning. Either course would lead to bloodshed. The conspirators would go ahead and kill Casear, and they would include Antony in the purge that followed Caesar's death. Or, on the other hand, Casear would use his soldiers to kill all the conspirators that Brutus named. It would seem to be to Brutus' best interest to warn Caesar if he decided not to participate in the conspiracy, because Brutus himself could easily become one of the victims of the conspirators if they succeeded in assassinating Caesar and gaining power. They would probably want revenge against Brutus for abandoning them. They might even think he had intended to betray them whether he did or not.