The New Hampshire high school student arrested after having sex with his girlfriend says he never knew he was breaking the law.

“I didn’t know there was a certain age you had to be to have sex,” said 18-year-old Damon Hadley of Henniker. “I thought if I told the truth, it’d all just go away.”

Hadley is set to tell his story on national television in an upcoming edition of ABC-TV’s “20/20” news show, according to his family and attorney. A spokesman for the show said it may air in March.

Hadley said he didn’t know he had committed a crime when he slept with his 15-and-a-half-year- old girlfriend last fall.

But he had.

And following what he said was his first sexual experience on Sept. 10, Hadley was charged with sexual assault and beaten by the girl’s father after she falsely claimed Hadley raped her.

Although she later admitted to police she lied about the rape allegation, Hadley had already admitted to a crime because, under state law, a person cannot consent to sex until the age of 16.

“When the (police) detective came to collect the bed sheets, Damon said ‘I knew the first time would be memorable, but I didn’t know it would be that memorable,’” said Lisa Hadley, Damon’s mother.

According to the Weare police prosecutor, the girl’s parents pushed for Hadley’s prosecution.

Last month in a plea deal, Damon Hadley pleaded guilty to simple assault, ending the legal case against him. The girl’s father – Gilberto Soto, 38, of Weare -- has also pleaded guilty to misdemeanor simple assault.

“I didn’t learn about (these laws) until this all took place,” said Lisa Hadley. “I don’t want anyone else to have to go through this.”

Damon Hadley said he agreed to the ABC television interview so people would hear his side of the story.

It started on Monday, Sept. 10. Hadley said he was taking a friend to get his driver’s license.

On the way, they picked up his girlfriend at school and later the two went back to Hadley’s house and had sex, he said.

Trouble began when Hadley and the girl tried to sneak back into school later that day. He said officials knew the girl had skipped school and the two students were separated and questioned.

Hadley said he was later told to return to class.

When he left school that afternoon, he saw his girlfriend’s father and brother waiting in a car. Hadley said the two jumped out and ran toward him.

“I didn’t move at all, I just froze,” Hadley said. “I didn’t know what to do. Her dad hit me. I was on the ground, I just remember him standing on top of me and hitting me.”

“He kept saying, ‘Did you (have sex with) my daughter?’” Hadley said as Soto hit him, the man’s son stood behind him watching. Hadley’s mouth filled with blood.

As other students left the building, some kept walking, others stopped to stare. Eventually, one of Hadley’s friends came and took him to the nurse’s office while the school resource officer pulled Soto away.

Hadley was later treated at the hospital for cuts and bruises and received two stitches to his face.

When Hadley went to the police station the next day to document his injuries, he learned the girl he’d been dating since June - the one he’d professed his love to - had accused him of rape.

The couple had been seeing each other in secret, he said, because her parents didn’t allow her to date.

After Soto and Hadley both pleaded guilty to misdemeanor simple assault, Soto was sentenced to 12 months in jail and Hadley to three months. Both sentences were suspended on condition of good behavior. Hadley said he’s not mad at his former girlfriend.

“There were parts when I was mad at her about the whole thing - why is she doing this, why is this happening to me,” Hadley said, then paused. “I don’t think I’m mad at her anymore. I hope she has a good life.”

He’s moved on, is dating someone new and supports his mother’s efforts to lobby both the state Legislature and local school boards.

Lisa Hadley wants schools to explain to students the laws regarding sex among minors.

She supports inviting police and lawyers into high schools to explain the consequences of engaging in underage sex.

“The work Lisa is doing and Damon is assisting her with, to educate the public, especially young people, is crucially important,” said Hadley’s lawyer, George Campbell, a Concord attorney with Robert Stein and Associates. “If the law is important enough to be enforced, it’s important enough that people be educated to not commit the act that’s been criminalized.”

Hadley will graduate from high school in the spring. He plans to take a year off and then pursue a degree in motorcycle mechanics at a technical college.