He has to smile. It doesn't matter how much he's hurting over Eddie's death, he has to stay strong. As much for himself as for his Marines. Eddie's death was a low point in the war for Andy, a low point in his entire life, and just seeing Haney fall apart like that almost brought him to tears right then and there. But he couldn't, at least not in front of his men, so he bit back his tears and pulled Haney away by a shaky hand and led him somewhere private. Somewhere away from the sad and judgemental eyes of the other men.
Andy can't quite remember what it feels like to be happy. The last time he was happy he was with Eddie. They were in their shared foxhole and Eddie had commented on something or another, Andy can't quite remember, but he remembers he laughed so hard he was crying and had to lean on Eddie for support. Then Eddie fell asleep on Andy's shoulder, and Andy will never forget that feeling. Andy will never forget any of the feelings Eddie had caused him to feel. Eddie wasn't only Andy's best friend, but he was his other half. His better half. And what were you supposed to do with only a half of yourself?
His heart hurt so much that he just felt like dying. Ever since Eddie left him, all he really felt like doing was following him into the afterlife. Andy might have been the captain, but he'd follow Eddie anywhere. And ever since Eddie was gone, Andy was lost. He was lost with no way of getting out. He knew he was going to die now. With no Eddie to keep him sane, and Haney already long gone down the path of insanity, Andy knew his time to crumble was coming soon. He wasn't scared in the least. He had embraced the fact that death was only the next adventure for him. And he knew that Eddie was waiting for him, and they would make the journey together.