Alexis was now staring at Captain Iroston very furiously. The Captain didn't know who Alexis was or why she cared about David, but seeing her getting angry at him like that made him take a step back. He did that without even realizing it because he was getting a sense of immense hostility from Alexis.
Colonel Amelia immediately held Alexis by her shoulders and then said to Iroston, "She is very close to David. I hope you can understand her emotion."
Iroston felt guilty when he learned that Alexis was someone who was close to David. He had to make a hard decision to leave David back on that planet. But he was trying to minimize his dissonance by saying to himself that he had made the right choice. However, seeing Alexis like that forced his mind to crumble down.