"You're not going to kill any of us, are you?" Agustín said. "For I will kill thee now." "Shut up," Pablo said. "I have to look after thy interest and that of the band. This is war. One cannot do what one would wish." (43.238-239)
Agustín is obviously disgusted by Pablo's murder of the men he brought with him. But Pablo's justification is that he was looking after the interests of their own band, since otherwise not all of them would be able to escape. Pablo's loyalties to his own small group are clearly much stronger than any duty he feels to his companions in the Republican cause; he's not only willing to kill fascists, he's willing to kill allies for the sake of his "tribe's" safety. Like those troubled by killing fascists, he ultimately lays the blame on the war situation itself.