After two teenage girls were killed by an Amtrak train last week, their deaths were ruled suicides by authorities. While the reason for their suicides was not known, experts who study suicides say people who are distraught — particularly young people — may seek out one another. "I think of it as the Romeo and Juliet phenomenon," said Jonathan Singer, an assistant professor of social work in Temple University’s College of Health Professions and Social Work. "You don't have the courage to do it by yourself . . . but when it's you or your best friend, it's strength in numbers."