A former Skyline High School teacher was sentenced Friday to eight years in prison for having a sexual relationship with a student.

Darryl Johnson Sr., 51, pleaded guilty to having an improper relationship between an educator and student, a second-degree felony. Visiting Judge Gary Stephens sentenced Johnson after a hearing Friday.

Darryl Johnson Sr. (Dallas County jail )

After Johnson was sentenced, one of his relatives pointed at his victim and shouted, "You will suffer."

The former student, now 21, wore a T-shirt with an image of Johnson while she testified. She said she still loves him.

She said their relationship began when she was a freshman at Skyline, where he was a teacher.

"I had a T-shirt made to symbolize my apology to you," the woman said.

The back of the shirt read: "Happiness is not overrated."

The front of the shirt had several codes printed on it, many of them Johnson used when messaging the girl while she was in high school.

"I knew it was wrong," she testified. "He knew it was wrong. It was a way to communicate without other people catching on."

Johnson is married with a son around the age of his victim.

She told police Johnson first had sex with her when she was 16. They were in his car. Johnson and the teen were involved in a sexual relationship between March 2012 and June 2014, police records show.

She reported the relationship in April 2016. During a recorded phone call between the girl's mother and Johnson, he claimed that he didn't have sex with the teen until she was 17 and a senior, police records show.

The victim told police that the relationship with Johnson continued until she was in college.

She testified Friday that she went to police after she suspected Johnson was beginning a relationship with another student.

"I just could not lose that to somebody younger than me," she said.

Defense attorney Angie N'Duka asked the judge to give Johnson probation in the case. She argued that he has been going through sex offender counseling. She said that prison wouldn't rehabilitate Johnson as well as the therapy he currently undergoes.

"A treated offender is better than a not-treated offender," N'Duka said.

But prosecutor Brandie Wade argued that the sentence should send a message that "educators are held to a higher standard."

"He was a teacher entrusted with the children of our community," Wade said. "Instead of growing and guiding, he groomed. Instead of protecting, he preyed."

Sex offender therapist Stacy Dupler described Johnson as a narcissist who was aroused by his victim when she was 14 and cultivated a relationship with her. He told Dupler that he waited until his victim was 17 before having sex with her.

Dupler said Johnson initially blamed the woman, saying she came onto him. But, Dupler said, she believed he was responding to treatment and would follow probation requirements.