Why did he do it?
Too driven by belief? A sense of righteousness?
He could have easily escaped, he was nothing more than a trap specialist who supported Sheva while marking down opponents or sometimes acting as a scout.
The kills in his hands were even lower, he rarely killed someone directly, instead, the opportunity to take life was always in Sheva's hand who did it covertly, and under his little diversion, she had the chance to escape before the enemies closed in on her position.
That was what they did as a team, he was never a hero, nor a warrior who could handle the soldier on his own.
No, if things had gone on as usual, he would not be babysitting Carp, a madman. Instead, he would be in Team One, along with others of his compatriots, enjoying the days as they do. But it would seem he was not blessed with such a life. He was too emotional, too weak of heart.