In all his time traveling with the courier, Boone had never seen them seriously hurt before. They were a dumbass who got into trouble constantly but Boone was always there to keep them safe. However, this time, Boone had failed.
They had made it all the way into Caesar's tent without injury, but that's when everything went wrong. Boone got distracted. He knew he shouldn't have, he never does, but he pulled his trigger too quickly. When the room eurrupted into chaos, Boone lost sight of the courier. He didn't care in the moment, only reveling in the joy of taking down legionaries like he always dreamed.
Once Boone had finished taking down the soldiers around him, he turned with a grin to see how courier was doing. But when he caught sight of them, his smile faded completely.
They were on the ground, overwhelmed by legionaries beside the dead body of Caeser. They were curled into a ball as soldiers landed kicked and punches unendingly. That's all Boone saw before everything went red.
Within the hour, Boone had successfully dragged the courier to safety while they were passed out. He sat beside them on an NCR cot, holding bandages in his hand as he examined their wounds. He had turned away every NCR soldier who tried to patch them up. It was his fault they got so hurt, so it was his responsibility to fix them.