A Sandown, N.H., teenager died in a collision Thursday night that left his girlfriend hospitalized with serious injuries, unaware that her boyfriend was killed.

Daniel Hendershot, 19, was killed in the collision on Route 121A in Hampstead, N.H. His passenger, Kaitlyn Sulivan, 20, was listed in fair condition at Massachusetts General Hospital.

Friends of the couple said that they were on their way home after picking up some milk when they slammed into another car. The two were recent graduates of Timberlane Regional High School, where the flag was at half-staff Friday.

"He seemed to be on his way," Principal Donald Woodworth said. "He was looking forward to a new job opportunity. He was going to do some training driving heavy equipment."

Woodworth said Hendershot and Sullivan were committed to each other.

"From all reports, it was very serious, perhaps getting married," he said.

Police said Hendershot's Honda Civic was headed north on 121A when it moved into the southbound lane, hitting another car with three women inside. Those three suffered more minor injuries and were being treated at area hospitals.

The head-on collision spun Hendershot's car around, throwing his girlfriend out of the passenger seat. She suffered several broken bones.

"It came at a time where you say, 'Here's a kid on a successful path,' and it's such a tragedy," Woodworth said.

Friends said Sullivan has been asking for Hendershot. They said the story has affected the entire school district, where one of their mothers works at the middle school and the other is a bus driver.

Police said they don't know what caused the collision, but Woodworth said he believes the car might have hit a patch of ice.