The Seven Network's Sunday Night program aired details of a letter Mrs Baden-Clay wrote to her husband, describing her "complete disbelief" about Gerard's affair with fellow real estate agent, Toni McHugh.

"What you had with her was not real," Mrs Baden-Clay wrote. "It was a boy's fantasy with an adrenaline rush every time you were sneaking about.

"You never, ever lived a reality with her. You were never with her when she had broken sleep for years on end as her children were little and she was breastfeeding. You only used her breasts for other f***ing reasons.

"You only saw her when she had washed her hair, shaved her bikini line, put her good undies on and was ready for her lover. That makes me bitter."

Despite her frustration, Mrs Baden-Clay wanted to save her marriage and made a list of things he could do.

She suggested they have weekly date nights, that he send her flowers and that he do "whatever it takes" to get their marriage back on track.

"Treat me with dignity and respect," she wrote.

Meanwhile, in a frank interview on Channel Nine's 60 Minutes, Ms McHugh said she believed her former lover had killed his wife, but did not believe he did so because he wanted to be with her.

Ms McHugh told the program he "killed for himself" and she remains "terrified", despite the life sentence handed down by the Supreme Court to the former Brisbane real estate agent.

"I'll never understand how it could have happened, I don't believe that he murdered her for me," she said, in what is understood to be a paid interview. "Why I say he did not kill her to be with me was that I loved him already. He didn't need to. He already had me."

Ms McHugh accepted she was one of the reasons Mrs Baden-Clay felt desperate and lonely as her marriage with Gerard crumbled. However, Ms McHugh deflected some of the blame, saying "if it wasn't me, it would have been someone else".

"He would have had affairs with other women," she said.

Ms McHugh said she was "devastated" and "absolutely concerned" when Mrs Baden-Clay was reported missing in April 2012 and initially believed the mother of three had run away.

"It was hard having to sit opposite him and have him staring at me, constantly, very coldly without feeling," she said of having to testify at his trial. "I want this man to never, ever, ever enter my life ever again. There is a part of me that is genuinely fearful that I have been involved with a man that is not who he says he is and that worries me. It terrifies me."

Baden-Clay was found guilty of his wife's murder on July 15, after a six-week trial in Brisbane.

The case against him was circumstantial, but evidence included a prosecution argument that his wife's life insurance payout would help his dire financial situation. They also argued scratch marks on his face were made by his wife as she struggled for life and blood found in the back of his car matched Mrs Baden-Clay's DNA.

Baden-Clay pleaded not guilty and has maintained his innocence.

He was sentenced to life in jail with a minimum non-parole period of 15 years. His legal team launched an appeal on July 17.