Dr. Petit says some people have tried to help him cope with grief by advising him to live in the moment. "I thought, 'That's okay for people who have a past they can touch and a future they can dream for,'" he says. "But when you feel like a lot of your past is gone and there's no future, the present loses some meaning."

Instead, Dr. Petit says he has found a reason to keep living—though he says he thought about suicide—through religion and faith. "I thought in the afterlife if I was going to meet up with my family, if I did that, then maybe I would never meet up with them again," he says. "I wasn't willing to take that chance."