By Selena Hernandez, CBS 11 News

IRVING (CBSDFW.COM) – A North Texas woman was sentenced to 45 years in prison Friday for killing her son.

Last May, Julianne McCrery, 42, drove from Iriving to New Hampshire where prosectutors say she suffocated her six year old child in a hotel room. She dumped his body along a dirt road in Maine.

Now, McCrery’s former boyfriend is speaking following her sentencing. He says he’s still struggling to find peace and understanding.

“I still haven’t found out why she decided to do this,” Robert Miller said.

It is the question that plagues Miller, and is perhaps one that will never be answered.

“He was an adorable child,” Miller said. “Everybody loved him dearly. He was a special child. He was funny and he was smart. He was a very nice little boy.”

Six-year old Camden McCrery wasn’t just a nice little boy. To Miller, Camden was practically his son. Miller dated the boy’s mother, Julianne McCrery.

“He called me R.D. – my initials,” Miller said. “But he would refer to me as his dad to other people.”

On Friday, Camden’s mother was sentenced to 45 years in prison for killing him. McCrery smother him in a New Hampshire motel, then left his body along a dirt road in Maine.

“I was shocked completely. This has actually shattered my life and the life of so many other family and friends.”

It is a sinister side of his ex-girlfriend Miller said he never suspected. A side that elicits both his concern and empathy.

“I think she should be in an instution for the rest of her life because I think she is really insane,” Miller said. “I don’t think Julie went up there just to kill him … I believe she intended for both of them to be dead.”

Miller says he doesn’t wish any ill will toward his ex-girlfriend. He just hopes McCrery can find proper treatment.

He says he hasn’t written or spoken to her in several months, but plans to reach out to her in the near future.