Newt was always the second in command. He was always putting others first, and he was always brave. He had to be, he couldn't let them lose hope because that was all they had, ever since the beginning. And after Alby was gone, and Gally had let them down, they followed Newt, and Newt followed Thomas. Then Thomas had come to him and told him he wasn't made to be leader, that he had no idea what he was doing. So Newt reassured him, because that was what he did, and he still didn't let his walls down. He still kept that brave face on.
Then he caught the Flare, and his world began to turn upside-down. But he still kept up his strong facade, putting Minho first even when he was slowly being eaten from the inside out. Even when Thomas kept giving him worried glances when he fell behind, when he leaned against a wall and began to cough black. He stood up tall, he smiled, he remained optimistic. But when Thomas pleaded to him, as his vision began to swim with darkness and his mind grew foggy, he screamed to be killed, to keep himself from hurting the other. But he wouldn't, that stubborn boy kept fighting, even when Newt pulled a gun to his head, he still stopped him. Even when his rotting body slashed at him with a blade, Thomas still didn't let up.
He was always strong, always brave, always levelheaded. Until he didn't need to be anymore. When it went dark, Newt was more than okay with having Thomas be the last thing he sees. He knows he left the others in good hands, he knows Thomas will be good to them.
He finally got to let go, finally got to rest.