Holcomb writes in a personal essay that Tyler had spoken to her about having children together and seemed happy with the pregnancy in the beginning.
Later on, however, his feelings changed and he pressured her to have an abortion.
Holcomb says Tyler raised the possibility of an abortion when she was recovering in hospital after nearly dying in a fire at their Boston apartment. She was five months pregnant by this time.
Even though she wanted to keep the baby, she says that Tyler told her she "needed" to have an abortion because of the damage to her health caused by the fire and because she was so young.
When she refused to have an abortion, Tyler told her to go back to her parents and have the baby there.
"I was five-months pregnant. I could not believe he was even asking me to have an abortion at this stage," she wrote in the article on LifeSiteNews.com.
"He spent over an hour pressing me to go ahead and have the abortion. He said that I was too young to have a baby and it would have brain damage because I had been in the fire and taken drugs. I became very quiet and repeated the answer 'No' more than once."
Fearful at the prospect of being rejected by Tyler and displeasing her parents, she caved in to the pressure.
Holcomb alleges that Tyler was snorting cocaine on the table beside her hospital bed as she was having the abortion, and even offered her some as she was undergoing the procedure.
"At the time I was shocked and hurt by his behaviour," she wrote. "But I know now that on an unconscious level, he must have been traumatised witnessing the death of his first-born son in such a horrific and direct way."
The injection induced contractions and the baby was born alive and left to die, she writes.
Holcomb has come to regret having the abortion.
"My baby had one defender in life: me, and I caved in to pressure because of fear of rejection and the unknown future," she said.
"I wish I could go back and be given that chance again, to say no to the abortion one last time. I wish with all my heart I could have watched that baby live his life and grow to be a man."
Tyler entered into a relationship with another woman not long after and Holcomb moved in with her mother and stepfather in Oregon.
Struggling with the grief and the recurring nightmares, she says a "turning point" came for her when she took part in a weeklong church retreat.
"I left there with a renewed sense of hope that God existed; He loved me in spite of my sins, and I could find forgiveness and a measure of real happiness within a family of my own if I began to rebuild my life," she said.
"I began to attend youth activities and the church became a lifeline that pulled me out of the fog of grief, sorrow, and guilt after my years with Steven."
She adds: "I prayed for the grace to forgive Steven."
Holcomb wrote the essay in response to Tyler's accounts of their relationship which she says are not true, such as claims that she had been pregnant before her relationship with Tyler and that she had had a previous abortion.
"I have made a point over these long years never to speak of him, yet he has repeatedly humiliated me in print with distortions of our time together," she said.
"I do not understand why he has done this. It has been very painful."
Despite this, the Roman Catholic mother-of-seven says she does not hate Tyler and is not bitter about what happened.
Instead, she is praying for him, for people who have had abortions, and for greater protection of the unborn.
"I pray for his sincere conversion of heart and hope he can find God's grace," she said.
"I know that I am also responsible for what happened that day.
"Someone may say that my abortion was justified because of my age, the drugs, and the fire. I do not believe anything can justify taking my baby's life. The action is wrong. I pray that our nation will change its laws so that the lives of innocent unborn babies are protected.
"I pray that all those who have had abortions, or have participated in any way in an abortion procedure, may find in my story, not judgment or condemnation, but a renewed hope in God's steadfast love, forgiveness and peace."