Jorge Fuentes did things his own way. “If you’re not being yourself, you’re not having fun,” he would say, flashing a smile. As a contrarian kid, he sometimes drove his mother and teachers and pastors crazy. But by his late teens, he was a standout counselor at his church’s youth programs. He traveled everywhere on mission trips, doing farm work in Virginia, feeding poor people in New York. He planned to join the Marines. Then, just over a year ago, came the stray shot, fired from a stranger’s gun, that hit the 19-year-old in the head as he walked his dog across the street from his family’s home in Dorchester.