(CNN) -- When an elated Remee Lee told her boyfriend she was pregnant, his reaction wasn't what she was expecting.

He wasn't happy, Lee says. In fact, he begged her to abort.

But it was her dream to have a child, Lee says. She never suspected that as she prepared for the new life, the man she loved was plotting to end it.

"I can't believe someone did something so malicious to me, and not only to me but to himself," Lee told CNN in May. "That was our baby."

This week, Lee's former boyfriend, 28-year-old John Andrew Welden pleaded guilty to killing their unborn baby. How? He tricked Lee to take an abortion pill, causing her to miscarry.

Guilty plea can't take away pain

Lee, 26, was in the Florida courtroom Monday, dabbing away tears as her former boyfriend accepted a plea deal that could send him to prison for at least 13 years.

Welden was indicted under the rarely used federal Unborn Victims of Violence Act, a murder charge that carries a life sentence.

Todd Foster, Welden's defense attorney, told reporters that the stakes of going to trial were too high.

"The possibility of a mandatory life sentence, no discretion to the judge, obviously is a big factor," Foster said. "Obviously it's tragic all around from every angle and I think that's recognized."

Those who know Lee say she's still burdened by sadness.

"Nothing is going to bring back what was taken from her," Lee's attorney Gil Sanchez said.

She trusted him

Lee said she was madly in love with Welden when she suspected she was pregnant.

"He was my everything. And more," she told CNN.

They went together for a sonogram at Welden's father's Tampa-area clinic. The test showed she was six weeks pregnant. Despite her boyfriend's reluctance, Lee planned to have the baby.

"Every woman dreams of becoming a mom," Lee said.

Days later, Welden told her blood tests had shown that she had an infection and needed to take amoxicillin.

But instead of the antibiotic, Welden brought her Cytotec, a drug that causes contractions.

Welden told her to take three pills a day. She trusted him.

After she took only one pill, Lee was rushed to the hospital with abdominal pain and bleeding.

She lost the baby. Doctors inspected the pills.

"Medical professionals saw that it wasn't quite right," Lee said. "Everybody knew it wasn't amoxicillin."

Welden said nothing as he left the courtroom Monday. Surrounded by security, he silently walked by a group of reporters, got into a black Hummer and was driven away.

Welden is scheduled to be sentenced December 5.