Bobby is one of those surprise characters – we start out hating him, and then wham! All of a sudden, we both like and respect him. Well then.
He replaces Rat as the team's medic, so automatically we (and the men) are wary of him. Then, he bungles Tim's wound so badly that Tim nearly dies of shock and gets gangrene of the butt.
But when we meet Bobby again a few months later, he's totally different. He owns up to his mistake, admits that it still gives him nightmares, and apologizes to Tim, but he doesn't debase himself. He doesn't make himself pathetic. And this makes Tim – and us – unable to hate the guy. When he and Tim are close at the end of "The Ghost Soldier," it feels right, unlikely the unholy partnership of Tim and Azar.