What it's like to be a young teen caught in an inappropriate teacher-student relationship

Jenny Kutner was in middle school when her history teacher started flirting.

Thomas has been missing since March 13. There has been speculation over whether Cummins and Thomas were in a romantic relationship together. Cummins, a married father and grandfather, researched teen marriage online, specifically the age of consent, according to law enforcement officials. A schoolmate reported seeing Thomas and Cummins kiss in his classroom on Jan. 23, according to a school district investigative report, but Thomas and Cummins denied the claim.

Cummins is wanted on allegations of aggravated kidnapping and sexual contact with a minor.

There’s a grim history of teachers abusing those in their care, turning a “school girl crush” into something sinister. Jenny Kutner experienced firsthand what it's like to be taken advantage of by a teacher.

Kutner, now 25, was 13 years old when her history teacher Lance Mueller started an inappropriate flirtation with her.

“It struck me as very innocent at the time, which now seems delusional,” she told "Nightline" co-anchor JuJu Chang. “I was very insecure. I had never had a boyfriend, I had never been kissed.”

At the time, Mueller was a 23-year-old teacher at Kutner’s middle school and engaged to be married. Kutner says she was bookish and more concerned with her classes than with cheerleading. So when Mueller first singled her out, she said she felt “really flattered” and “really special.”

“I felt that he really saw me, which was a feeling that I didn't have often among the teenage boys,” she said. "He felt so mature and I felt that I was so mature for my age."

Despite their 10-year age gap, Mueller spent time with Kutner individually in his truck, eventually coming to her house when her parents weren’t around.

“I can’t remember a moment during a given day in that period when I wasn’t speaking with him except for when I was in class,” Kutner said. “He started using pet names pretty early, always referred to me as ‘babe’ or ‘baby, ‘sweetheart.’”

Soon, she said, the manipulation escalated.

“He was telling me that we were in a relationship, and he was telling me that he loved me more than his wife,” she said. “He would say that if I ever left him that he might have to kill me because he couldn’t imagine anyone else being with me or he would have to kill himself for the same reason -- very manipulative things.”

And then, right after her 14th birthday, at which point she was in high school, Kutner said the relationship crossed the line from highly inappropriate to criminal. They got sexual in her bedroom, again when her parents were away.

“I felt that I was the one asking for this relationship to go further,” she said. “I was the one who wanted him in my bedroom.”

At the time, Kutner said, she blamed herself for instigating their relationship, but now she says she knows better.

“The ‘grooming’ occurs not so that an abuser can propose some sort of sexual behavior, it’s almost so that the victim is the one that suggests it,” she said.

Kutner finally confided in friends about the relationship, who then told her parents. In shock and horror, her parents called the police.

“It was very traumatic,” she said. “At the time, it felt like I was very much choosing to be involved in this. I also knew that he had more of the upper hand in the situation. But either way, it very much felt that he was pursuing me.”

After lengthy legal proceedings, Mueller pleaded guilty to sexual assault, spent 180 days in jail and was placed on the sex offender registry.

It took Kutner years to accept she was a victim. “I understood rationally, pretty early on, when I was still in high school, but the only thing that made me grasp emotionally what had happened to me was time,” she said.

Kutner says she now realizes what she endured was classic manipulation and coercion. When it’s a young student and a teacher, who is in the power position, Kutner said she doesn’t believe it’s possible for the student to give consent and understand the consequences, despite how the teenager may feel at the time.

“Not in a true and meaningful sense, certainly not in a legal sense,” she said.

“While it might feel like you are able to consent to that,” she added, “you're still too young to understand those power dynamics and to understand just how much it does influence your own decision making that this person is an authority figure ... for years and years throughout your schooling you've been conditioned to listen, to obey, to respect.”

Kutner was one of the lucky ones whose relationship was flagged to her parents. Speaking up in these situations is critical, she said. If bystanders think they witnessed something inappropriate, perhaps a student spending a lot of extra time around the teacher or the teacher spending time with the student outside of school, then it’s good to raise concerns.

“Your gut will usually tell you that something is just not right,” Kutner said.